Apparatus and methods for removing a large-signal voltage offset from a biomedical signal

ABSTRACT

Apparatus and methods remove a voltage offset from an electrical signal, specifically a biomedical signal. A signal is received at a first operational amplifier and is amplified by a gain. An amplitude of the signal is monitored, by a first pair of diode stages coupled to an output of the first operational amplifier, for the voltage offset. The amplitude of the signal is then attenuated by the first pair of diode stages and a plurality of timing banks. The attenuating includes limiting charging, by the first pair of diode stages, of the plurality of timing banks and setting a time constant based on the charging. The attenuating removes the voltage offset persisting at a threshold for a duration of at least the time constant. Saturation of the signal is limited to a saturation recovery time while the saturated signal is gradually pulled into monitoring range over the saturation recovery time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/718,996, filed Dec. 18, 2019, which is a divisional of U.S. patentapplication Ser. No. 16/195,562, filed Nov. 19, 2018, which claims thebenefit of U.S. Provisional Patent Application No. 62/669,345, filed May9, 2018, entitled “Acquisition and Preservation of Electrical SignalInformation in a Multi-Signal-Source Environment,” all of which arehereby incorporated by reference.

TECHNICAL FIELD

Embodiments included herein generally relate to cardiacelectrophysiology (EP) signal acquisition and recording systems. Moreparticularly, apparatus and method embodiments are disclosed forremoving a large-signal voltage offset from a biomedical signal.

BACKGROUND

Catheter ablation is a procedure to treat arrhythmias such as atrialfibrillation, a disease of the heart muscle characterized by abnormalconduction. Depending on the severity of the problem, multiple ablationprocedures may be necessary to achieve effective results. This isbecause current electrophysiology (EP) technology has limitations inprecisely locating the tissue to ablate that is the source of theabnormality.

The conventional diagnostic process starts with an electrocardiogram(ECG) taken from electrodes attached to the surface of the skin of asubject (e.g., a patient). A medical team evaluates the ECG signal anddetermines whether medication and/or ablation are/is indicated. Ifablation is indicated, an EP study is performed. A catheter is insertedinto the heart via the patient's neck or groin and the electricalactivity of the heart is recorded. Based on this EP study, ablation isperformed on the area(s) of the heart that the medical team suspects iscausing the abnormal heart rhythm(s).

An ablation catheter is inserted into the patient's blood vessel andguided to the site of the tissue that is causing the abnormal electricalpropagation in the heart. The catheter may use different energy sources(the most common being heat or cold) to scar the tissue, reducing itsability to initiate and/or transmit abnormal electrical impulses, whicheliminates the abnormal heart rhythm. ECG signals are recorded from asurface electrode on a patient's skin, and intracardiac (IC) signals maybe obtained from catheters inside the patient's heart and recorded as anelectrogram (EGM). Both ECG and IC (EGM) signals are small signals thatrequire conditioning and amplification to be accurately evaluated.

In conventional EP systems, to confirm whether the ablation treatment ofa certain tissue site is successful, the medical team must often stopthe ablation process and collect physiologic signals (e.g., cardiac)from a monitoring device (e.g., ECG monitor). This is because currentsystems do not allow accurate simultaneous detection, acquisition, andisolation of small cardiac signals (on the order of 0.1-5 mV over arange of frequencies) in near real-time during the application of largeablation signals (on the order of a few hundred volts at frequenciesaround 450 kHz).

Specifically, U.S. Patent Application Publication No. US 2006/0142753A1to Francischelli, et al. propose a system and method for ablation andassessing their completeness or transmurality by monitoring thedepolarization ECG signals from electrodes adjacent to the tissue to beablated. Francischelli, et al. point out that, to minimize noise-sensingproblems during measurements of the ECG signals from the electrodes onthe ablation device, the measurements are preferably made duringinterruptions in the delivery of ablation energy to the ablationelectrodes.

Generally, some current EP recording systems can effectively supporttreatment of arrhythmias such as atrial flutter and supra ventriculartachycardia, which show up as large-amplitude, low-frequency signals.However, more complex and prevalent arrhythmias, such as atrialfibrillation and ventricular tachycardia, which are characterized bylow-amplitude, high-frequency signals, have not found effectiveevaluation of all relevant signals.

This signal detection, acquisition, and isolation can be furthercomplicated by equipment line noise and pacing signals. To remove noiseand artifacts from the various electrical signal information, current EPrecorders use low-pass, high-pass, and notch filters. Unfortunately,conventional filtering techniques can alter signals and make itdifficult or impossible to see low-amplitude, high-frequency signalsthat can be inherent in cardiac monitoring, the visualization of whichsignals could help treat atrial fibrillation and ventriculartachycardia. It has been recently recognized that the assurance ofwaveform integrity, such as for noise-free acquisition of IC and ECGsignals in an EP environment, had not been previously accomplished dueto contamination of various signals by artifacts and noise.

Specifically, in an article titled Waveform Integrity in AtrialFibrillation: The Forgotten Issue of Cardiac Electrophysiology (Annalsof Biomedical Engineering, Apr. 18, 2017), Martinez-Iniesta, et al.point out that high-frequency and broadband equipment noise is“unavoidably recorded” during signal acquisition, and that furthercomplications of acquisition result from a variety of other signals,including 50 or 60 Hz electrical mains, high-frequency patient muscleactivity, and low-frequency baseline wander from respiratory or cathetermovements or unstable catheter contact. Martinez-Iniesta, et al. furtherpoint out that regular filtering causes significant alteration ofwaveforms and spectral properties, as well as poor noise reduction. Yetaggressive filtering between 30 and 300 Hz is still a routine EPpractice.

Conventional practices distort morphological features in resultingsignals, causing loss of relevant (of interest) signal information andaffecting signal validity. Martinez-Iniesta, et al. propose a partialsoftware solution for only mid- and high-frequency noise reduction usingpreprocessing and de-noising methods, yet no solution exists combininglow-frequency noise-reduction components in software withnoise-reduction components in hardware. A desired feature of EP systemsis the ability to preserve the integrity of original signal informationusing a combination of hardware and software that can remove noise fromsignals (or promote a high signal-to-noise ratio) while minimizinghardware filtering that would otherwise remove signal content ofinterest.

Currently, the predominant approach for ablation treatment of paroxysmaland persistent atrial fibrillation is pulmonary vein isolation (PVI),wherein a medical team, using a cardiac mapping system, recreates theheart geometry in 3D and performs ablation on anatomical locations suchas the pulmonary vein from which the atrial fibrillation emanates. Theprocedure is a long 2-8 hours, and a physician may not achieve a durablelesion/scar to isolate the tissue causing the problem from the leftatrium. Thus, patients are often required to return for additionalablation procedures to complete the treatment. However, additionalablation procedures, and possible complications, can be avoided by beingable to clearly visualize the cardiac signals during ablation anddetermine whether an ablation lesion is transmural.

Conventional EP systems may suffer from several other limitations.First, a user often wants to process and display multiple versions ofsignals in near real-time. For example, a medical team may want tosimultaneously display various and multiple versions of ECG, IC, andother physiologic signals in near real-time to evaluate different signalattributes. But conventional EP systems are often unable tosimultaneously process and display multiple versions of signals in nearreal-time.

Second, a user often wants to dynamically apply a new digital signalprocessing function to a signal without interfering with other digitalsignal processing functions already being applied to the signal. Butconventional solutions do not enable a user to dynamically apply a newdigital signal processing function to a signal without stopping thecapture of the signal, or interfering with other digital signalprocessing functions already being applied to the signal.

Finally, a user often wants to synchronize the processing and display ofmultiple signals in near real-time. For example, a user may want tosynchronize the display of multiple processed versions of the samesignal. Further, a medical team may want to synchronize the display ofmultiple processed versions of ECG, IC, and other physiologic signals.This is because the ability of the medical team to make an effectiveclinical diagnosis may depend on comparing multiple signals at the samepoint in time. But conventional solutions may not be able to process andsynchronize the display of multiple processed signals in near real-time.

SUMMARY OF THE EMBODIMENTS

Apparatus, systems, and methods are disclosed for EP signal acquisitionand recording with multiple improvements in noise cancellation, samplingrate, and dynamic range in various biomedical applications.

The embodiments of the disclosed EP system can record raw (unaltered)cardiac and other physiologic signals with multiple display options andwith low noise and large input signal dynamic range. This is achievedusing a low-noise amplifier topology, with minimal filtering toband-limit the signal, and a high-resolution A/D converter. In addition,the disclosed EP system can provide large-signal (e.g., from adefibrillator) input protection and radio frequency (RF) signal (e.g.,from ablation) noise suppression. In this architecture, there is no needfor gain switching, and the full range of input signals is digitizedwith high resolution.

Raw signals acquired by an acquisition module are filtered and processedin accompanying software using a digital processing module, with minimaluse of filters in the hardware (e.g., hardware filters are only used forAC coupling, anti-aliasing, and RF suppression). The use ofsoftware-based digital signal processing algorithms allows the displayof signals in real-time as a raw signal, or as a combination of raw andprocessed signals simultaneously in real-time in a single window or inmultiple windows. Furthermore, the visualization and review capabilitiesof the disclosed EP system allow a user to mark features specified inalgorithms on real-time tracings.

The disclosed EP system allows for the display of signals with more thanone signal processing algorithm applied at the same time, a feature notfound in conventional systems. This allows a user to look at signalsfiltered in multiple ways for specific reasons. In the real-time window,waveforms of interest can be displayed as raw signals or as anycombination of raw and filtered signals to enable better visualizationof signals in the presence of noise and artifacts.

All displayed signals are time synchronized. On a review screen, theuser has the option of opening multiple review windows, with the abilityto display the results of various signal-processing algorithms,independent of the real-time tracings. The disclosed EP system also usesnovel optimal biphasic waveforms and signal processing algorithms forsignal enhancement during pacing, and novel algorithms for enhanced uservisualization.

From a clinical perspective, the disclosed EP system can significantlyassist in a medical team's decision making for patients undergoingvarious medical therapies (such as ablation), with benefits including,but not limited to: suppression of RF energy for cleaner, more reliablerecordings of intracardiac signals, less wander, and noise reduction;improved dynamic range for better visualization, especially of very lowamplitude signals temporally situated within large-amplitude signals;real-time digital processing and recording of raw signals to facilitatesignal filtering without affecting original information and to reduceartifacts and noise; high-quality unipolar signals to assist in thedetermination of tissue type and catheter location; improved waveformintegrity and reduced artifacts that are byproducts of signalprocessing, allowing a medical team to enhance procedure outcomes; andimproved signal information, allowing a medical team to provide moreaccurate catheter tip position for ablation and other therapeutic levelsand durations for therapy effectiveness.

Some embodiments herein describe a circuit for removing a large-signalvoltage offset from a biomedical signal. The circuit includes a firstoperational amplifier having a differential input and a differentialoutput, and is configured to receive the biomedical signal with thelarge-signal voltage offset at the differential input. The circuit alsoincludes a second operational amplifier having a common mode voltageinput and configured to output a common mode reference voltage at acommon mode node. A first pair of diode stages is coupled between thedifferential output and respective ones of a first differential node anda second differential node and is configured to monitor an amplitude ofthe large-signal voltage offset. A plurality of timing banks is coupledbetween the respective ones of the first differential node and thesecond differential node and the common mode node. The first pair ofdiode stages and the plurality of timing banks may be configured toattenuate the large-signal voltage offset persisting for a duration ofat least the time constant, wherein the large-signal voltage offset isabove an activation threshold. Further, a second pair of diode stages iscoupled between the respective ones of the first differential node andthe second differential node and the common mode node, wherein thelarge-signal voltage offset is attenuated at an output of each of thesecond pair of diode stages. The second pair of diode stages isconfigured to limit a saturation duration of the large-signal voltageoffset to shorter than a saturation recovery time.

Various method embodiments are described for removing a voltage offsetfrom an electrical signal (e.g., a biomedical signal in someembodiments), including receiving, at a differential input of a firstoperational amplifier, the electrical signal, and amplifying, by thefirst operational amplifier, the electrical signal by a first gain.Method embodiments include monitoring, by a first pair of diode stagescoupled to a differential output of the first operational amplifier, anamplitude of the electrical signal for the voltage offset. Further, themethod embodiments include attenuating, by the first pair of diodestages and a plurality of timing banks, the amplitude of the electricalsignal. The attenuating includes limiting charging, by the first pair ofdiode stages, of the plurality of timing banks from the electricalsignal and producing, by the plurality of timing banks, a differentialsignal. The attenuating further includes charging of aresistor-capacitor network of the plurality of timing banks and setting,by the plurality of timing banks, a time constant based on the chargingof the resistor-capacitor network. The method allows for attenuating theamplitude of the differential signal to remove the voltage offsetpersisting at an activation threshold for a duration of at least thetime constant.

Some method embodiments include limiting, by a second pair of diodestages, the differential signal from the plurality of timing banks andfurther limiting a saturation duration of the differential signal toless than a saturation recovery time. Some method embodiments furtherinclude pulling an output voltage of the second pair of diode stagestoward a common mode reference voltage at a common mode node coupled tothe plurality of timing banks. Some method embodiments may includepulling, by the second pair of diode stages, a positive input nodevoltage of the first operational amplifier down toward the common modereference voltage and a negative input node voltage of the firstoperational amplifier up toward the common mode reference voltage. Somemethod embodiments further include limiting, by the second pair of diodestages, the differential signal from the plurality of timing banks,wherein the positive input node voltage and the negative input nodevoltage are gradually pulled into monitoring range after about thesaturation recovery time.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present embodiments and, togetherwith the description, further serve to explain the principles of thepresent embodiments and to enable a person skilled in the relevantart(s) to make and use the present embodiments.

FIG. 1 illustrates a block diagram of a conventional electrophysiology(EP) environment with patient connections and sources of interference.

FIG. 2 illustrates a hardware system block diagram of the disclosed EPhardware system, according to some embodiments.

FIG. 3 illustrates a block diagram of a multi-channel analog-to-digitalinput/output of the EP hardware system input stage, according to someembodiments.

FIG. 4 illustrates a block diagram of a single channel of the EPhardware system input stage, according to some embodiments.

FIG. 5A illustrates a block diagram of the overall EP system, accordingto some embodiments.

FIG. 5B illustrates a high-level abstraction of the overall EP systemhardware and software, according to some embodiments.

FIG. 6A illustrates a schematic diagram of the large-signal inputprotection portion of the input protection circuit of the EP hardwaresystem, according to some embodiments.

FIG. 6B illustrates a schematic diagram of the electrostatic discharge(ESD) protection portion of the input protection circuit of the EPhardware system, according to some embodiments.

FIG. 7 illustrates a schematic diagram of the radio frequency (RF)filtering portion of the input protection circuit of the EP hardwaresystem, according to some embodiments.

FIGS. 8A-8E illustrate voltage signal plots of a typical defibrillationsignal at the input to the input protection circuit, according to anexemplary embodiment.

FIGS. 9A-9E illustrate voltage signal plots of a typical ablation signalat the input to the input protection circuit, according to an exemplaryembodiment.

FIG. 10 illustrates a schematic diagram of the instrumentation and gainstages of the EP hardware system, according to some embodiments.

FIG. 11 illustrates a schematic diagram of a large-signal detection/fastrecovery circuit of the EP hardware system, according to someembodiments.

FIG. 12 illustrates a voltage signal plot showing the slow recovery thatoccurs after a large unwanted signal survives the input protection,instrumentation, and gain stages of the EP hardware system circuitrywhen the large-signal detection/fast recovery circuit is disconnected,according to an exemplary embodiment.

FIGS. 13A-13C illustrate voltage signal plots showing the fast recoverythat occurs after a large unwanted signal is presented to the inputprotection, instrumentation, and gain stages of the EP hardware systemcircuitry when the large-signal detection/fast recovery circuit isconnected, according to an exemplary embodiment.

FIGS. 14A-14D illustrate signal plots for voltage signals at variousinternal nodes through the large-signal detection/fast recovery circuitwhen it is connected, according to an exemplary embodiment.

FIGS. 15A-5B illustrate signal plots for current signals over theresistors at the output of the connected large-signal detection/fastrecovery circuit, according to an exemplary embodiment.

FIG. 16 illustrates a schematic diagram of a low-frequency feedbackcircuit that serves as a dynamic current source for the EP hardwaresystem, according to some embodiments.

FIGS. 17A-17D illustrate signal plots for typical in-band voltagedifferential input signals that are affected by 60 Hz common-mode noiseinto the EP hardware system, according to an exemplary embodiment.

FIGS. 18A-D illustrate signal plots of a typical differential voltagesignal affected by 60 Hz common-mode noise as it travels through the EPhardware system, according to an exemplary embodiment.

FIGS. 19A-D illustrate signal plots of a typical 500 kHz ablation inputsignal that is in a frequency range to be attenuated by the RF filter ofthe EP hardware system, according to an exemplary embodiment.

FIGS. 20A-20B illustrate signal plots of a typical 500 kHz ablationinput signal at the shield inputs that enable the RF filter to attenuatethe input signal to the EP hardware system, according to an exemplaryembodiment.

FIGS. 21A-21D illustrate signal plots of a typical 500 kHz ablationinput signal that has been attenuated after it has traveled through theinstrumentation amplifier and after it has traveled through the fullydifferential op amps of the EP hardware system, according to anexemplary embodiment.

FIG. 22A illustrates the improvement in the visualization of an ECG orIC signal, according to an exemplary embodiment.

FIG. 22B illustrates the EP system's ability to reveal low-amplitudecardiac signals and micro-components of artifacts of an EP signal in thepresence of noise and large-signal procedures, according to an exemplaryembodiment.

FIG. 22C illustrates the EP system's ability to remove 60 Hz noise,without saturation or delayed recovery, while preserving the componentof the 60 Hz signal that belongs to the original waveform, according toan exemplary embodiment.

FIG. 23 illustrates a schematic diagram of an improved Wilson CentralTerminal-Right Leg Drive (WCT-RLD) circuit, according to someembodiments.

FIG. 24 illustrates a schematic diagram of a Twin-T feedback networkinterfaced with an RLD circuit of a WCT-RLD circuit, according to someembodiments.

FIG. 25 illustrates a signal plot of the output of a Twin-T feedbacknetwork of a WCT-RLD circuit, according to an exemplary embodiment.

FIG. 26 is a block diagram of a system for processing and displayingmultiple signals in near real-time, according to some embodiments.

FIG. 27 is a block diagram of a queuing module for the storage ofgenerated packets associated with different base signals, according tosome embodiments.

FIG. 28 is a block diagram of a configuration path module for generatingat runtime time-aligned signals that are processed from a set of basesignals, according to some embodiments.

FIG. 29 is a block diagram of a signal module generated by a signalfactory module, according to some embodiments.

FIG. 30 is a block diagram of a display module for displaying one ormore signals, according to some embodiments.

FIG. 31 is a block diagram of a monitoring module for performing errorchecking, according to some embodiments.

FIG. 32 illustrates an example adjustment of a sweep speed for a displaymodule, according to some embodiments.

FIG. 33 illustrates signal management for a display module, according tosome embodiments.

FIG. 34 illustrates an example adjustment of zoom and clip factors for adisplay module, according to some embodiments.

FIG. 35 illustrates pattern searching for a display module, according tosome embodiments.

FIG. 36 illustrates a late potential search of a display of a displaymodule, according to some embodiments.

FIG. 37A illustrates using a waterfall view via a display module,according to some embodiments.

FIG. 37B illustrates using a waterfall view via a display module,according to some embodiments.

FIG. 37C illustrates using a dynamic view via a display module,according to some embodiments.

FIG. 37D illustrates using a trigger view via a display module,according to some embodiments.

FIG. 38 illustrates the capture of a display of a display module,according to some embodiments.

FIG. 39 illustrates the visual analyzation of a captured display of adisplay module, according to some embodiments.

FIG. 40 is a flowchart for a method for processing and displayingmultiple signals in near real-time, according to an embodiment.

FIG. 41 is a flowchart for a method for configuring one or more signalmodules, according to some embodiments.

FIG. 42 is a flowchart for a method for generating a signal module froma signal processing specification, according to some embodiments.

FIG. 43 is a flowchart for a method for equalizing the processing delayassociated with each DSP of the one or more signal modules, according tosome embodiments.

FIG. 44 is a flowchart for a method for receiving one or more signalsamples for one or more signals using an input module, according to someembodiments.

FIG. 45 is a flowchart for a method for converting one or more signalsamples to one or more packets using a packetizer, according to someembodiments.

FIG. 46 is a flowchart for a method for dispatching a packet containingone or more signal samples to a queueing module, according to someembodiments.

FIG. 47 is a flowchart for a method for dispatching a packet from aqueuing module to a signal module associated with the packet, accordingto some embodiments.

FIG. 48 is a flowchart for a method for processing a packet using asignal module associated with the packet, according to some embodiments.

FIG. 49 is a flowchart for a method for displaying a processed packet toa display screen using a display module, according to some embodiments.

FIG. 50 illustrates an example computer system, according to someembodiments.

The features and advantages of the present embodiments will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The drawing in which an elementfirst appears is indicated by the leftmost digit(s) in the correspondingreference number.

DETAILED DESCRIPTION OF THE INVENTION

Apparatus, systems, and methods related to a unique amplifier topologyare disclosed for conditioning cardiac (e.g., ECG and IC) and otherphysiologic signals, specifically to clearly define and recordlow-amplitude, low-frequency information, which may be acquired duringablation and other similar large-signal perturbations, such as pacingand stimulation. During procedures, the tip of a catheter (or otherelectrodes) can be connected to pacing, ablation, and stimulator systemsto allow visualization, pacing, ablation, and stimulation without modeswitching. For example, the disclosed apparatus, systems, and methodscan effectively separate ablation signals from cardiac signals duringablation while simultaneously providing input protection against highvoltage, such as from defibrillation signals. Similarly, the disclosedapparatus, systems, and methods can effectively separate stimulationsignals from physiologic signals during stimulation.

As different system recording requirements cannot be satisfiedsimultaneously for each signal type, each block, or module, of thesystem can be performance optimized to achieve multiple signalconditioning requirements desired by clinicians. The various embodimentscan enable the system to handle cardiac, pacing, ablation,defibrillation, stimulator, and other physiologic signal typessimultaneously by detecting, conditioning, and displaying the signal ofinterest, to monitor, for example, the effect of an ongoing procedure ona cardiac signal.

Additionally, the various embodiments can ensure the acquisition ofmultiple low-amplitude cardiac signals in the presence of numeroussources of electrical noise and environmental interference aside fromthe large signals injected during ablation and stimulation procedures,pacing, or defibrillation. The cardiac signals of interest can also bedisplayed in an uncomplicated and clinically-relevant way, processingthe signals in real-time, or near-real-time, to display a comprehensivecause-and-effect relationship between physician-initiated procedures andresulting cardiac signals, while contemporaneously identifying signalartifacts and removing unwanted noise. This disclosure identifies bothhardware and software embodiments to achieve these objectives.

This disclosure refers to both “unipolar” and “bipolar signals,” whichare both widely used in EP recordings, but for complementary purposes.Both unipolar and bipolar signals are taken from the potentialdifference recorded at two (or more) different, separated electrodes ona patient's body, specifically the limbs and chest of the patient, forexample, to measure ECG signals, or at two (or more) different,separated catheters placed directly on cardiac tissue, for anotherexample, to measure IC signals.

It is conventional to use a 12-lead ECG system consisting of aconnection to each of the limbs: right arm (RA), left arm (LA), rightleg (RL), and left leg (LL), and six precordial connections V1 throughV6 from six separate electrodes placed at various locations on thepatient's chest. The individual ECG electrode wires are connected to aterminal block at the end of a patient table, routing from there to adata acquisition system. All leads are conventionally connected toprotection circuitry to prevent damage to the instrumentation caused bydefibrillation potentials or static electricity from the environment.

Bipolar signals are standard for certain ECG measurements (lead I, II,III), but they may also be obtained directly from the heart surface tocollect IC signals. Bipolar signals may be obtained by attaching two (ormore) electrodes in close proximity in a specific area of the heart orcardiac tissue and measuring the potential difference between theelectrodes, providing information about local electrical activity, suchas late potentials caused by damaged heart muscle. Bipolar IC signals donot, however, provide information about electrical impulse propagationdirection.

Unipolar signals arise from a point source, such as may be obtained froman IC potential, by placing one IC electrode on the surface of thepatient's heart and the other electrode at a distance from the first toserve as a reference signal. Unipolar leads from IC electrodes areconnected in such a way that one lead serves as the active lead whilethe other lead(s) is/are at an inactive location or the result of acalculated inactive location (WCT, discussed below). In this way, thecurrent flowing towards the active electrode produces a positivedeflection, while current flowing away from the active electrodeproduces a negative deflection. This provides information about cardiacsignal propagation direction. Unipolar recordings are especially usefulwhen directionality information is desired, such as in the determinationof depolarization and repolarization pathways in the endocardium andepicardium.

Leads may also be connected to the limbs to create an imaginary trianglecalled “Einthoven's triangle.” In this way, true bipolar leads can beobtained by referencing each connection to one of the other two (e.g.,LA referenced to RA is Lead I; LL to RA is Lead II, and finally, LA toLL is Lead III). Then, an average of the three limb wires RA, LA, and LLcan approximate a zero potential point to provide a reference electrode(WCT, discussed below). Here, the vector sum of Lead I and Lead III isLead II.

Using the concept of Einthoven's triangle, the Wilson Central Terminal(WCT) is an electrical circuit concept used in the art (and discussedfurther in this disclosure) that can be used as an indifferent electrodethat acts as an electrical center of the heart as a reference. The WCTcan be used when IC signals are desired to be displayed in unipolarfashion. When using the WCT as a reference for unipolar signals, theunipolar signals can approximate widely-spaced bipolar signals forconsistent unipolar recording. The WCT can prevent an additionalcatheter from having to be used as a reference for unipolar recordingsof IC signals.

In this disclosure, “near real-time” refers to the acquisition andvisualization of signals through the EP system from the time they occurat the input of the hardware circuitry of the EP system to the time theyare first displayed on the EP system display monitor(s), either in raw(unprocessed) form or after being processed by the EP system MainProcessing Unit (MPU) and one or more digital signal processing (DSP)module(s). “Near real-time” for a raw signal can be less thanapproximately five (5) milliseconds, and for a processed signal can beless than approximately fifty (50) milliseconds.

FIG. 1 is a block diagram representing a conventional EP environment 100with patient connections and sources of interference. As understood by aperson of ordinary skill in the art, the patient 118 may be connected todiagnostic equipment such as a pulse oximeter 104, one or more ECG units106, an infusion pump 108, an electroanatomic mapping system 110, a dataacquisition system 112, such as the EP system disclosed herein, anablation generator 114, a nerve stimulator 128, and other diagnosticequipment, such as an external defibrillator, and several IC catheters.Such diagnostic equipment can be connected to and can be powered by120-240V, 50/60 Hz AC power mains 102. The laboratory diagnosticequipment can be connected to earth ground 120, through its power sourceconnection.

As the number of connections to the patient 118 increases, the leakagecurrent 122 from all patient connections through the patient 118 toearth ground 120 increases, increasing the likelihood of interferenceand adverse effects. Total leakage current 122 when such equipment isconnected and operating at the same time may safely and allowably be upto several tens of microamperes at a fundamental mains frequency of 50or 60 Hz, with harmonics extending to several thousand Hertz. Thisleakage current 122 can interfere substantially with the processing ofECG and IC signals. Furthermore, the patient 118 can be bothcapacitively coupled 124 and inductively coupled 126 to the 120/240 ACpower mains 102. The patient 118 may additionally pick up RFinterference 116 from equipment in proximity to the EP environment, suchas wireless headsets, mobile phones, and wireless monitors.

For reference, TABLE 1 outlines signals that may be found in aconventional medical instrumentation/EP environment, both wanted andunwanted, and their signal characteristics.

TABLE 1 Signal characteristics in a conventional EP environment SignalAmpli- Nature/Use of Signal Type tude/Output Frequency Signal ECG(cardiac 0.5 to 4 mV 0.01 to 250 Conventionally skin electrodes) Hzrequired for cardiac monitoring IC (intracardiac 20 μV to 10 0.05 to 500Conventionally leads) mV Hz required for cardiac monitoring EGG 10 μV to1000 DC to 1 Hz Smallest biomedical (electro- μV signal of interestgastrography) (non-EEG) RF Ablation RF output: 100 300-600 kHz,Conventional System W, 100 s of V 460-500 kHz equipment used typicalduring EP study Defibrillation 4500 to 5000 V 10 s of ms Possibleequipment duration used in EP environ- ment Pacing Cardiac 0.1 to 25 mA,0.5 to 10 ms Conventional Stimulator 27 Vmax duration; up equipment usedduring to 1000 μs EP study pulse width; up to 1200 Hz Equipment 2 Vpptypical 60 Hz, 180 Hz Conventional lab power-line harmonic environmentpower noise

As a result of equipment noise and other EP environment interference,measured voltages on a patient's body can be upwards of 1-3 V RMS (rootmean squared) over a frequency spectrum ranging from 50 Hz to severaltens of megahertz. Yet, the amplitude of cardiac signals can measure inthe range of 25 microvolts to 5 mV. To display these signals amongst thenoisy environment, the cardiac signals are conventionally amplified anddisplayed with no loss of detail (so as not to miss relevantinformation, for example) and minimal added noise (so as not to cover upsignal details, for example), while delivering RF ablation energy atabout 70 V RMS at 500 kHz, or cardiac stimulation up to 25 mA, forexample.

To properly acquire and identify cardiac signals of interest in such anenvironment, a very high signal-to-noise (SNR) ratio (on the order of 30dB) is desirable but not achievable without an approach to minimize oreliminate sources of electrical interference before having to processthem electrically through software methods. Conventional hardwareapproaches used to condition the signals in such a noisy environmentinclude shielding of cables, grounding of equipment, balancing inputsand outputs, differential amplification, filtering, lowering circuitimpedances, electric isolation, or signal enhancement techniques. Theseconventional methods have had limited success in achieving sufficientSNR.

The disclosed hardware embodiments can decrease interference whileapplying novel electrical circuit topology to minimize noise, isolatethe IC and ECG signals of interest, condition those signals, and removeunwanted artifacts. This can be done before the signals are passed toprocessing software that provides an electrophysiologist the power ofnear real-time visualization and comprehensive signal review.Embodiments of the EP system described herein can achieve considerableSNR improvement.

FIG. 2 is a hardware system block diagram representing the disclosed EPhardware system 200, including, for example, an EP workstation 201 andan EP console 214, according to some embodiments. The system can includean EP console 214 with an optical interface 216 of the EP measurementhardware from a user input, visualization, and review workstation(herein, “EP workstation” 201). The EP workstation 201 can include, forexample, a conventional laboratory PC 208 with a keyboard/mouse 210 anda monitor splitter 206 facilitating multiple monitors 202, 204 toprovide multiple-signal, multiple-context display capability for EPsignal visualization and review software. The EP workstation 201 canalso include an additional optical interface 212 for electricallyisolated data transmission from the EP console 214 over USB 2.0, forexample.

The EP console 214 can include one or more ECG amplifiers 218, one ormore unipolar amplifiers 220 to process unipolar signals, and one ormore bipolar amplifiers 222 to process bipolar signals from a pluralityof ECG and EGM monitoring units 224. The EP console 214 can also includea dedicated AC input filter 234, a AC/DC power supply 236, and a DC/DCpower supply 238 to condition and transform mains 120/240 V, 50/60 Hzsource power 240 into DC power for use by the diagnostic equipment. ECGand EGM electrode inputs 232 can enter the EP console 214 through a yoke226 that provides additional input impedance for protection. Junctionboxes (1 and 2) 228, 230 can provide convenient plug-in interfaces forIC catheter inputs (not shown) for subsequent processing by EGMmonitoring units 224.

FIG. 3 is a block diagram representing a multi-channel analog-to-digitalinput/output module 300 of the EP hardware system input stage, includingan ECG board 302 and an IC board 316, according to some embodiments. TheECG board 302 and the IC board 316 represent a portion of the ECGamplifier 218, unipolar amplifier 220, and bipolar amplifier 222 of FIG.2. The ECG board 302 and the IC board 316 include a plurality of EPhardware system input stage 400 channels, discussed below (see FIG. 4).FIG. 3 illustrates one (1) 8-channel ECG board and one (1) multi-channelIC board, according to an exemplary embodiment. Some embodiments have atleast sixteen (16) channels. Other embodiments can include more or fewerchannels.

In FIG. 3, analog inputs V1-V6 304 represent six separate ECG(precordial) electrodes that can be placed at various locations on thepatient's chest. Analog inputs LL, RA, and LA 306 represent the leftleg, right arm, and left arm limb leads, respectively. Analog output RL308 represents the patient return line to drive the right leg, asdiscussed later in this disclosure. WCT 314 on the ECG board 302, alsodiscussed later in this disclosure, represents the Wilson CentralTerminal, which also uses the analog inputs LL, RA, and LA 306. Theoutput of the WCT 314 can then be input to each channel of the EPhardware system input stage 400 corresponding to the analog inputs V1-V6304. Each of the digital outputs V1-V6 310 represents a conditioned anddigitized version of the respective analog inputs V1-V6 304. In anexemplary embodiment, digital outputs I, II 312 can include LAreferenced to RA as lead I, and LL referenced to RA as lead II, in aconditioned and digitized form. Then, an average of the three limb wiresLL, RA, and LA 306 can approximate a zero potential point to provide areference level for the generation of RL 308.

In FIG. 3, a plurality of analog inputs to the IC board 316 representpossible connections and channels through the EP hardware system inputstage 400 (see FIG. 4) from the intracardiac catheters. The IC board 316can accept IC signals that are either unipolar or bipolar. INDIF 318represents the indifferent electrode, which provides a reference for aplurality of unipolar indifferent leads. ICUniWCT1, 2, through N signals320, represent unipolar IC signals referenced to the WCT. ICUniINDIF1,2, through N signals 322, represent the active electrode of each ICunipolar signal. ICDiff1, 2, through N signals 324, represent aplurality of the bipolar differential signals from IC catheters. Aplurality of digital outputs represents the conditioned and digitizedversions of the analog inputs, specifically ICUniWCT1, 2, through Nsignals 326; ICUniINDIF1, 2, through N signals 328; and ICDiff1, 2,through N signals 330.

FIG. 4 is a block diagram representing a single channel of the EPhardware system input stage 400, having circuitry for input protection,signal filtering, detection, feedback, and amplification, according tosome embodiments. The circuitry is illustrated in the block diagram bynumbered blocks 1 through 11, each representing a part of thefunctionality of the hardware. This division and labeling of blocks isfor ease of description and not meant to limit the scope of protectionafforded by the appended claims. The input protection and signalfiltering sections of the EP hardware system input stage 400 includesymmetric positive and negative circuitry to generate differentialversions of each input signal for a differential signal amplificationstage 532, described below.

FIG. 5A is a block diagram 500 of the overall EP system disclosedherein, according to some embodiments, generally showing the interfaceof the Main System Unit (MSU) (hardware components) 504 to the MainProcessing Unit (MPU) (software components) 514. FIG. 5A is discussed inmore detail later in this disclosure.

FIG. 5B is a block diagram 524 representing the main sections of the EPhardware system input stage 400, with sections 530, 532, 534cross-referenced to sections shown in the EP hardware system input stage400.

In FIG. 5B, the analog input protection/filtering stage 530 includesBlock 1—Input Protection 402 a, Block 2—RF Filter 404 a, Block 3—Buffer406 a, Block 4—DC Block 408 a, Block 10—Low Frequency Feedback 420 a,and Block 11—Shield Drive 422 a. The symmetric negative circuitryincludes Block 1—Input Protection 402 b, Block 2—RF Filter 404 b, Block3—Buffer 406 b, Block 4—DC Block 408 b, Block 10—Low Frequency Feedback420 b, and Block 11—Shield Drive 422 b. The signal amplification stage532 includes differential circuitry that includes Block5—Instrumentation Amplifier/Filter 410, Block 6—Differential Amplifier1/Filter 412, Block 7—Differential Amplifier 2/Filter 414, and Block9—Large Signal Detection/Fast Recovery 418. The A/D converter stage 534includes Block 8—the A/D Converter 416. The A/D converter stage 534 alsoincludes a communication module 510 (shown in FIG. 5A) that can formatthe signals for transmission over fiber optic link 512 to the DigitalProcessing Stage 528, represented in some embodiments by the MPU 514.

The functionality of the specific Blocks 1-11 of FIG. 4, a singlechannel of the EP hardware system input stage 400, is described in thefollowing paragraphs.

Analog Input Protection/Filtering Stage

The analog input protection/filtering stage 530 of the EP system, shownin FIG. 5B, includes Block 1—Input Protection 402 a, 402 b; Block 2—RFFilter 404 a, 404 b; Block 3—Buffer 406 a, 406 b; Block 4—DC Block 408a, 408 b; Block 10—Low Frequency Feedback 420 a, 420 b; and Block11—Shield Drive 422 a, 422 b. These elements, according to someembodiments, are described in more detail in the following paragraphs.

Input Protection Circuitry

FIGS. 6A, 7, and 6B illustrate circuits that include the analog inputprotection/filtering stage 530 of the disclosed EP system, according tosome embodiments. FIG. 6A illustrates the overvoltage protectioncircuitry 600 (represented by Block 1 (402 a, 402 b) in FIG. 4), whichcan protect the other EP hardware system input stage 400 circuits fromlarge transient voltages, specifically, for example, from defibrillationpulses. The analog input protection/filtering stage 530 can protectagainst an input voltage that is out of the range of what the circuitscan practically handle.

Specifically, the analog input protection/filtering stage 530 can reducehigh voltage transients at the ECG, IC, and other electrode lead inputs,which are connected to the patient's body, to less than ten (10) volts,for example, at the inputs to the EP system buffers. The analog inputprotection/filtering stage 530 can stop a large signal, for example,from a defibrillator, from damaging other portions of the system. Inaddition, the analog input protection/filtering stage 530 can performthese functions without sinking more than 10%, for example, of theenergy of an applied defibrillation pulse, without clamping, or withoutadding non-linearities when ablation signals are applied.

FIG. 6A illustrates an exemplary embodiment of Block 1's overvoltageprotection circuitry 600, including an off-the-shelf gas discharge tube(GDT) 608 that can fire at very high voltages, such as voltages above300 V, to provide high voltage surge protection. GDT 608 is coupled totwo stages of diodes 610, 612 (and resistors 602, 604) designed tosequentially clip the signal to 18 V, for example, to remove adefibrillation signal of up to 5000 V, for example. Diodes 610 representan off-the-shelf electrostatic discharge (ESD) voltage suppressor devicethat can aid the GDT 608 until the GDT 608 is fully on. Diodes 612represent an off-the-shelf bidirectional ESD protection diode that canlimit the In2 input of the RF filter (Block 2) to 18 V at the nodelabeled (a) in FIGS. 6A and 7.

Conventionally, a defibrillation signal of approximately 5000 V would beclamped to +/−5 V to prevent harm. In the case of this disclosure,defibrillation signals can be similarly clamped, but ablation signalswith an ablation voltage of approximately 200 V at 500 kHz, for example,can be passed linearly and attenuated by the input resistors RCable,602, 604 and Block 2 (FIG. 4, 404 a, 404 b), the RF filter 702.

FIG. 7 illustrates an RF filter/shield drive 700, including an RF filter702 and a shield drive 730. The RF filter/shield drive 700 connects tothe overvoltage protection circuitry 600 of FIG. 6A at the node labeled(a) for the transmission of signal In12 through the analog inputprotection/filtering stage 530. The RF filter 702 of the RFfilter/shield drive 700 is described in more detail below. The shielddrive 730 of the RF filter/shield drive 700 is also described below.

The input overvoltage protection circuitry 600 does not clamp theablation signal; rather, the ablation signal is attenuated linearly(e.g., reduced in direct proportion by the input resistors RCable, 602,604 and RF filter 702) so that it is not inadvertently altered. Forexample, if the ablation signal is clamped by the input overvoltageprotection circuitry 600, there would be no further access to thecontents of that signal above the clamping. Advantageously, linearattenuation of the ablation signal by the disclosed EP system can permitrecording small cardiac signals of a few millivolts during ablation. Aperson of ordinary skill in the art will appreciate that the apparatus,systems, and methods disclosed herein apply similarly to otherhigh-frequency signals that may need to be passed through the protectioncircuit (e.g., not clamped) to prevent generation of non-linearitiesthat would affect the signals of interest.

FIG. 6B represents ESD input protection circuitry 620 at the finalsection of the analog input protection/filtering stage 530. The ESDinput protection circuitry 620 is coupled to the RF filter/shield drive700 at the node labeled (b) of FIG. 7. An ESD protection chip 622 canprovide ESD protection up to 30 kV for data lines and can respond toovervoltage conditions in nanoseconds. Any number of off-the-shelf ESDprotection devices can be used for this purpose.

Transient voltage suppressor (TVS) diodes 628, 630 can provide ESDprotection exceeding 16 kV by shunting excess current when the inducedvoltage exceeds their breakdown voltage. TVS diodes 628, 630 canfunction as “clamping,” or limiting, devices to suppress an overvoltageabove their breakdown voltage and can automatically reset when theovervoltage subsides. TVS diodes 622, 630 can also respond toovervoltages faster than other common overvoltage protection components;e.g., “clamping” occurs in about one picosecond. TVS diodes generallycan be advantageous for protection against very fast and potentiallydamaging voltage transients.

FIGS. 8A-8E and 9A-9E illustrate sample signal plots to demonstrate howthe front-end input protection circuitry handles high voltage transientsand ESD, according to an exemplary embodiment. FIG. 8A illustrates thevoltage of a representative defibrillator signal, V(Defib), that isapplied to the input of the input protection circuit labeled “EPsignals” in FIG. 6A. In a laboratory setting, the defibrillator signalcan be derived by applying 5000 volts to a 32 μF capacitor and thendischarging the capacitor to the connected electrodes on the patient.Because of inductance and resistance, the amplitude received at theelectrodes is approximately 4500 volts lasting some tens ofmilliseconds.

FIGS. 8B-8E illustrate the different voltage levels as thedefibrillation signal proceeds through the circuit. V(In) of FIG. 8B isthe voltage on GDT 608 of FIG. 6A. GDTs have very low capacitance (e.g.,less than 1 pF) and high impedance (e.g., greater than 100 MOhms) in theoff state. They function as a gap between two electrodes. When GDTsionize and turn on, they may have very low resistance (e.g., a few Ohms)with large current carrying capability (e.g., carrying 10 s of amperes);thus, they act as a short circuit. A disadvantage of GDTs is that theycan take some time to turn on, as the plot for V(In) in FIG. 8B shows.GDTs should trigger at 230 V, but the voltage rises to a much higherlevel before they turn on effectively and start to conduct. Turn-on timecan be several hundred nanoseconds. A resistor RCable in FIG. 6A limitsthe current going into the GDT 608. This can reduce the power that isdissipated in the system and can also ensure that the analog inputprotection/filtering stage 530 does not shunt any appreciable powermeant for the patient.

The ESD voltage suppressor diodes 610 in FIG. 6A can turn on muchfaster, within a nanosecond, for example, but have a lower power/energycapacity such that they can activate quickly. They can hold the voltageat P1, as shown in the signal plot for V(P1) of FIG. 8C, to around 30 Vwhile the GDT 608 turns on fully. When the GDT 608 is on fully, the ESDvoltage suppressor diodes 610 are no longer active.

The next stage in FIG. 6A is a bidirectional pair of ESD protectiondiodes 612 that can limit the signal at In12, the input to the RF filter(Block 2), to approximately 18 V, as shown in the signal plot for V(In12) of FIG. 8D. The signal through the RF filter is further describedbelow in the RF filter (Block 2) section.

Finally, as shown in FIG. 6B, at In13, after the signal has beenfiltered by the RF filter of Block 1, an ESD protection chip 622 canclip the signal at VDD+/−a diode drop (e.g., +/−5.7 volts), as shown inthe signal plot for V(In13) of FIG. 8E.

A person of ordinary skill in the art will understand that thecombination of input protection circuitry shown in FIGS. 6A and 6B,including GDT 608, diodes 610, diodes 612, ESD protection chip 622, andTVS diodes 628, 630, protects the circuitry of an EP recording system.However, this circuitry by itself can be detrimental to achieving aquality EP recording during ablation. For example, if the ablationsignals were clipped, the non-linearities produced may cause noise andmask the cardiac signals of interest. Because a medical team may want tosee the cardiac signals during ablation, the integration of the Block 2RF filter with the input protection circuitry is an improvement overconventional solutions. The disclosed embodiments allow unwanted andpotentially disruptive or damaging signals to be attenuated whilelinearly filtering an ablation signal and monitoring ECG and IC signals.

For example, FIGS. 9A-9E are signal plots that illustrate theprogression of an ablation signal through the input protection circuitof FIGS. 6A, 7, and 6B. The ablation input is 400 Vpp at the sensorelectrodes, as shown by plot V(Defib) in FIG. 9A. As the signalprogresses through the stages of the input protection circuit, thesignal is attenuated by the resistor RCable (shown as FIG. 9B plotV(In)), resistor 602 (shown as FIG. 9C plot V(P1)), resistor 604 (shownas FIG. 9D plot V(In12)), and capacitor 716 (shown as FIG. 9E plotV(In13)). The ablation signal voltage levels are 100 Vpp at node In ofFIG. 6A, 12 Vpp at node In12 of FIG. 6A, and 60 mV at node In13, afterthe RF filter of FIG. 7. The ablation signal does not trigger theprotection devices, but is attenuated linearly, permitting observationand/or recording of the cardiac signals during ablation. The ablationsignal can be further filtered at each of the Block 5, 6, and 7 of thesignal amplification stage 532 (see FIGS. 4, 5B, and FIG. 10), and atthe A/D converter (Block 8 in FIG. 4) that has a 100 dB low-pass filterat 950 Hz.

RF Filter Circuitry with Low-Frequency Feedback and Shield Drive

In addition to its contribution to the input protection circuitry tofilter and linearly attenuate ablation signals at the EP system input,RF filter 702 can function in concert with the low-frequency feedbackcircuit of Block 10 (see FIG. 4, 420 a and 420 b, and FIG. 16, 1600) toenable the overall circuit to continue linear attenuation of ablationsignals (e.g., with voltage amplitude of about 200 V in the frequencyrange of about 300 kHz to about 600 kHz) during cardiac monitoring, innear real-time, while passing small cardiac signals (e.g., having afrequency range of about 0.01 Hz to about 500 Hz), for example.

The RF filter 702 can be designed to linearly attenuate the amplitude ofthe ablation signal by at least 75% in some embodiments, or even by atleast 90% in other embodiments, for example. The RF filter 702 can bedesigned to provide substantially no attenuation to an input signalhaving a frequency less than 5 kHz, for example. This RF filter 702 canalso function in concert with the shield drive 730 of Block 11 (see FIG.4, 422 a and 422 b, and FIG. 7), which can work with input capacitors706, 714, 716 of RF filter 702 to help maintain high input impedance ofthe overall circuit. This high input impedance can help minimize theinput losses of the cardiac signal of interest. The shield drive 730 isfurther discussed below.

Low-Frequency Feedback Circuit

Block 10 (see FIG. 4, 420 a and 420 b), a low-frequency feedback circuit1600, can provide positive feedback to the Block 2 RF filter (see FIG.4, 404 a and 404 b, and FIG. 7, 702) to increase input impedance to theEP system, thus reducing signal attenuation. This is advantageousbecause the input impedance of the EP system in the frequency range ofthe cardiac signals can be compromised by the RF filter 702.

Specifically, high input impedance at the instrumentation amplifier 1001of FIG. 10 can be greatly reduced depending on the frequency of theinput signal (e.g., by a factor of 100 at 60 Hz) by the presence of theRLC network elements 706, 708, 714, 716 of the RF filter 702. Althoughthe RF filter 702 is advantageous at ablation frequencies, reduction ofimpedance at low frequencies can reduce the amplitude of the cardiacsignals and affect common mode rejection. Without mitigating the effectof the RF filter 702, the advantages of the instrumentation amplifier1001 would otherwise be lost.

To mitigate that loss and maintain high common mode rejection (e.g., onthe order of 100 dB), it is desirable to maintain high impedances at thepower line frequencies so that variations in source impedance do notconvert common mode signals into differential signals. The Block 10low-frequency feedback circuit 1600 illustrated in FIG. 16 receives thebuffered version of the signal of interest from the Block 3 buffer 406a, 406 b as Buf1 1602. The low-frequency feedback circuit 1600 thenapplies operational amplifier 1606 to drive Shield1 728 at the base(that is, bottom plate) of the capacitors 706, 714, 716 in RF filter702. Specifically, the operational amplifier 1606 serves as a driver toeliminate loading effects and maintain the high input impedance of theanalog input protection/filtering stage 530 into the signalamplification stage 532.

When the Block 10 low-frequency feedback circuit 1600 drives the RFfilter 702 at low frequencies, there is little or no voltage variationacross the capacitors 714, 716. Thus, at low frequencies, capacitors706, 714, 716 act as open circuits and the high input impedance ismaintained. But at higher frequencies, the feedback from the Block 10low-frequency feedback circuit 1600 is reduced due to the low-passfiltering functionality of Block 10.

Specifically, the combination of a capacitor 1666 and a resistor 1693 atthe inverting input to the operational amplifier 1606 filters highfrequencies. The output of this circuit no longer tracks the input andholds the Shield1 728 (also the reference node of the RF filter 702) toa fixed level with respect to high frequency signals. This enables theRF filter's 702 passive RLC network 706, 708, 710, 712, 714, 716 toattenuate the high frequency signals.

Specifically, the Block 10 low-frequency feedback circuit 1600 (see alsoFIG. 4, 420 a and 420 b) takes the buffered signal from the Block 3Buffer circuit (see FIG. 4, 406 a and 406 b) and produces a correctingsignal to Shield1 728 of FIG. 7, that is, the equivalent of the input asa feedback signal at the capacitors 706, 714, 716 of the Block 2 (seeFIG. 4, 404 a and 404 b) RF filter 702. This feedback to the capacitors706, 714, 716 is provided as a dynamic current source for the circuit.

The RF filter 702 of Block 2 404 a, 404 b is enabled for filtering athigh frequencies, but the RF filter 702 is disabled at low frequencieswhen receiving feedback from the low-frequency feedback circuit 1600 ofBlock 10 420 a, 420 b. At high frequencies, the capacitors 706, 714, 716in the RF filter 702 function as shunting capacitors that effectivelyshort circuit signals at RF frequencies. The impedance of the capacitors706, 714, 716 decreases linearly as the frequency becomes higher. Thelow-frequency feedback circuit 1600 does not affect the EP system athigh frequencies.

At low frequencies, the low-frequency feedback correcting signal,Shield1 728 from Block 10 (see FIG. 16) to Block 11 (shield drive 730 ofFIG. 7), drives the bottom plates of the capacitors 706, 714, 716, suchthat these capacitors mimic the input signal. This controls thereference node of the RF filter 702. Specifically, the voltage at theplates of the capacitors 706, 714, 716 vary in sync with each other, andthe low-frequency feedback circuit 1600 drives the bottom plate of thecapacitors 706, 714, 716 of the RF filter 702 to be the same voltage asthe upper plate, such that the voltage difference at the plates of thecapacitors 706, 714, 716 becomes zero and the capacitors 706, 714, 716act as open circuits.

The goal of the low-frequency feedback is to drive the differencebetween Shield1 728 and Buf1 1602 to zero, such that Shield1 728 equalsBuf1 1602. When this occurs, input capacitance can be eliminated. Athigh frequencies, the positive feedback from operational amplifier 1606is reduced to zero. In addition, at high frequencies capacitor 722(which is 30 times larger than other capacitors in the circuit, forexample) acts as a short circuit between Shield1 728 and ground. Thiseffectively grounds the reference node of the RF filter 702, fullyenabling it to attenuate RF frequencies. Thus, the Block 10low-frequency feedback circuit 1600 works in concert with a uniquearrangement of the Block 2 RF filter 702 elements to remove the loadingeffect of the RF filter 702 before passing signals to the Block 5instrumentation amplifier 1001.

In this manner, the instrumentation amplifier 1001 can condition cardiacsignals without the overlying ablation signal. The result is that theinput to the overall circuit at low frequencies still sees a very highinput impedance (e.g., on the order of 10s of MOhms) that isadvantageous to visualizing high-fidelity cardiac signals in an EPenvironment. Additionally, Block 10 is a symmetric (e.g., mirrored)circuit, so that common mode noise is subtracted as the signalpropagates through the circuit. Another advantage of the low-frequencyfeedback circuit 1600 is that its output Shield1 728 can be used todrive the outer shields of the input cables, for example, at OutS1 ofthe shield drive 730 of FIG. 7.

Shield Drive Circuit

Block 11 (see FIG. 4, 422 a and 422 b), specifically the shield drive730, shown in FIG. 7, receives the output of the low-frequency feedbackcircuit 1600 (Shield1 728 of FIG. 16) of Block 10 (see FIG. 4, 420 a and420 b) and provides positive feedback to the cable shields at OutS1,thus reducing the effective input capacitance of the input cables.Therefore, the path from the bottom plate of the input capacitors 714,716 in the RF filter 702 of Block 2 (see FIG. 4, 404 a and 404 b), tothe shields of the input cables, further contributes to making the inputimpedance as large as possible. This high input impedance minimizes theinput losses of the cardiac signal of interest. In some embodiments, theshield drive connections are grounded if a shield drive is not desired.

Signal Buffering and DC Blocking Circuitry

Block 3 (see FIG. 4, 406 a and 406 b) is a low-noise unity gain driverthat aids in minimizing the input losses of cardiac signals.Specifically, it can provide the high input impedance to minimize theload of the input stage to the cardiac signals and to drive the signalamplification stage 532. In Block 3, two operational amplifiers (circuitnot shown) form two buffers that serve as a unity gain follower thatbuffers the input and gives the input a high input impedance.

Block 4, the DC Block (see FIG. 4, 408 a and 408 b), is a high-passmodule (circuit not shown) that prevents input offsets from thesensor/tissue interface of the patient's body from entering theamplifier gain stages. In Block 4, two DC blocking capacitors (notshown) immunize the input from the large offsets from catheters.

Signal Amplification Stage

The signal amplification stage 532 (see FIG. 5B) of the EP systemincludes differential circuitry: Block 5—InstrumentationAmplifier/Filter 410, Block 6—Differential Amplifier 1/Filter 412, Block7—Differential Amplifier 2/Filter 414, and Block 9—Large SignalDetection/Fast Recovery Circuit 418. These circuits are described inmore detail in the following paragraphs.

Instrumentation Amplifier/Filter Circuitry

Block 5 (see FIG. 4, 410) is an instrumentation amplifier/filter thatprovides amplification to the differential signal and common moderejection of unwanted signals, specifically, power line noise andrelated harmonics, from the equipment laboratory or medical environment.Block 5, detailed in FIG. 10, has a gain stage 1001 with a differentialgain of about 20 at its output, and it provides additional filtering forRF attenuation through its RC network 1008, 1010, 1012, 1014. Twooperational amplifiers 1006, 1016, for example, are low-noise devices,designed to receive cardiac signals at the input to the instrumentationamplifier 1001, before the cardiac signals have been amplified. Thedifferential signal from the Block 5 instrumentation amplifier 1001 thenenters the precision resistor block 1018 of the Block 6 differentialamplifier #1 1017.

Differential Amplifier/Filter Circuitry

Block 6 (see FIG. 4, 412) has a differential amplifier 1020 thatproduces a fully differential output with a unity gain, as referenced tocommon mode voltage. Block 6 differential amplifier #1 1017 can provideadditional filtering for RF attenuation. Maintaining a fullydifferential signal path helps reduce noise from entering from thedigital part of the system. Such noise would appear mainly as commonmode noise and get rejected. This part of the signal amplification stage532 also shifts the DC bias of the cardiac signal from 0 up to 2.5 V andlimits its output from 0 to 5 V.

At an output of Block 6, having a first fully differential amplifier1020 referenced to common mode, the common mode level is set to 2.5 V asthe signals enter Block 7 differential amplifier #2 1021. The circuitcontinues the low-pass filtering of the ablation signal to the outputs(B2OutP, B2OutN) of Block 7. Block 7, having a second fully differentialamplifier 1034 similar to Block 6's differential amplifier 1020, has again of about 0.5, with additional filtering for RF attenuation providedby circuit elements 1022, 1024, 1026, 1028, 1030, 1032, 1036, 1038,1040, 1042. This part of the signal amplification stage 532 maintainsthe fully differential signal path to continue rejection of noise.

The gain introduced by Block 7 allows the circuit to clip the signal atthe input limits of the A/D converter, Block 8 (see FIG. 4, 416), whichcan be a delta-sigma converter (not shown), for example. As previouslymentioned, the Block 6 differential amplifier #1 1017 clips each outputsignal to +/−2.5 volts relative to the bias level of 2.5 volts. Withgain of 0.5, the outputs of the Block 7 differential amplifier #2 1021produce signals biased at 2.5 volts with a range of +/−1.25 volts foreach output, or 2.5 volts peak-to-peak differential. This represents thelimits of a 24-bit A/D converter 416, for example, in some embodiments.By clipping and matching the output limits, the input of the A/Dconverter 416 is prevented from being overdriven. Because a delta-sigmaconverter can behave erratically when overdriven, potentially causingspurious results, it is advantageous that the embodiments allow the fullrange of inputs to the A/D converter, but no more.

The overall gain of the signal amplification stage 532 of the disclosedEP system can be less than or equal to 20 in some embodiments, or can beless than or equal to 50 in other embodiments, for example. For example,in some embodiments, a gain of about 20 at the output of theinstrumentation amplifier 1001, a unity gain at the output ofdifferential amplifier #1 1017, and a gain of about 0.5 at the output ofdifferential amplifier #2 1021 produce a system gain of about 10 at theinputs of the A/D converter 416. Generally, the signal amplificationstage 532 can include an instrumentation amplifier 1001 with a gaingreater than one (1) at its output, a differential amplifier #1 1017with a gain of about one (1) at its output, and a differential amplifier#2 1021 with a gain of less than one (1) at its output.

The overall low gain of the system, due to its improved ability toremove noise, provides further improvement over conventional systems.Conventional systems that have a 16-bit A/D converter require high gainin order to visualize small signals that are obscured in the presence ofhigher-amplitude signals. Conventional systems can have gain of up to5000, for example, causing saturation of signals to occur quickly.Further, if lower gain is used with a 16-bit converter, quantizationnoise can adversely affect the output results. With the disclosed systemhaving a low gain of about 10, coupled to a 24-bit A/D converter,saturation is prevented until at least 250 mV, for example, ofsmall-signal input, and quantization noise is avoided.

Fast Recovery/Large-Signal Detection/Fast Recovery Circuitry

The outputs from the Block 6 differential amplifier #1 1017, in additionto being passed to the Block 7 differential amplifier #2 1021, also arepassed to Block 9 (see FIG. 4, 418 and FIG. 10), the large-signaldetection/fast recovery circuit 1100 of FIG. 11. The large-signaldetection/fast recovery circuit 1100 can remove large signals andrecover quickly from large transients. This circuit is thus called a“fast recovery” circuit because of its improved ability to recover fromsaturation much faster than conventionally achieved.

Specifically, the large-signal detection/fast recovery circuit 1100 candetect that the differential input signal has been in excess of 100 mV,for example, for a duration of at least 10 milliseconds, which isidentified as an abnormal operating range. On detection of this state,the large-signal detection/fast recovery circuit 1100 can reduce thetime constant after the Block 4 DC blocking stage (see FIG. 4, 408 a and408 b) to ensure that the cardiac signal does not remain in saturation.But, the large-signal detection/fast recovery circuit 1100 can havenegligible effect under normal operation. For example, the large-signaldetection/fast recovery circuit 1100 can have no effect on fasttransients produced by pacing, which can be a signal of interest tomonitor and record in an EP environment, and which can have transientsthat last generally less than 10 milliseconds.

In an embodiment, the first stage of the large-signal detection/fastrecovery circuit 1100 has two operational amplifiers 1108, 1112, forexample. The gain of the operational amplifier 1108 (e.g., about 40)determines the activation threshold, that is, at which signal amplitudethe large-signal detection/fast recovery circuit 1100 can operate tolimit (or “soft clamp”) a signal. The activation threshold determineshow large the signal must be before the large-signal detection/fastrecovery circuit 1100 becomes active and begins to pull the voltages atnodes In14 and In24 toward the common mode level. For example,operational amplifier 1108, with a gain of about 80, can activate thelarge-signal detection/fast recovery circuit 1100 at about 50 mV; with again of about 40, can activate the large-signal detection/fast recoverycircuit 1100 at about 100 mV; and with a gain of about 20, can activatethe large-signal detection/fast recovery circuit 1100 at about 200 mV.When the signal amplitude reaches the set amplitude level determined bythe gain, the voltage will be enough to overcome the activationthreshold of a first pair of diode stages 1114, 1116 to activate thelarge-signal detection/fast recovery circuit 1100.

Operational amplifier 1112 produces a unity gain to buffer the commonmode (CM) signal, which provides a common mode reference for the signalsthrough operational amplifier 1108. Operational amplifier 1108 receivesU4Out1 and U4Out2 signals from Block 6 (see FIG. 10). Accordingly, theaverage of the U4Out1 and U4Out2 signals is referenced to the commonmode node (CMB of FIG. 11). The signals out of operational amplifier1108 pass through the first pair of diode stages 1114, 1116 that limitthe charging of the subsequent capacitors 1120, 1124, 1128, 1132. Thesecapacitors 1120, 1124, 1128, 1132, which accumulate a charge from thebuffered U4Out1 and U4Out2 signals, produce the maximum positive (+) andnegative (−) charges for both the inverting and non-inverting version ofsignals U4Out1 and U4Out2.

The capacitors 1120, 1124, 1128, 1132 form an RC network at nodes C, D,E, and F with resistors 1118, 1122, 1126, 1130, which together serves asa timing network that determines a time constant. The time constantdetermines how long the signals can be at their maximum amplitude beforethe large-signal detection/fast recovery circuit 1100 pulls the voltagesat nodes In14 and In24 toward CM. This RC network is hereinafterreferred to as “timing banks” 1158. Some embodiments of the timing banks1158 may be designed to produce a time constant of at least 10milliseconds, for example, to prevent activation of the large-signaldetection/fast recovery circuit 1100 during pacing signals of2-milliseconds to 10-milliseconds duration, for example. Otherembodiments may be designed to produce a time constant of at least five(5) milliseconds.

When the capacitors 1120, 1124, 1128, 1132 charge up, a difference isdetected, and the signal passes through a second pair of diode stages1146, 1148, which limits (or “soft clamps”) the input to between about+/−100 mV, for example. This prevents the system from saturating for anyappreciable amount of time (e.g., less than 100 milliseconds). Thesecond pair of diode stages 1146, 1148 also ensures that there is nointeraction between the large-signal detection/fast recovery circuit1100 and the EP system if a signal is not large/long enough to requirelimiting. In other words, when it is not advantageous to activate thelarge-signal detection/fast recovery circuit 1100, the second pair ofdiode stages 1146, 1148 disconnects the large-signal detection/fastrecovery circuit 1100. The Block 9 large-signal detection/fast recoverycircuit 1100 ensures that the EP system is not affected by large signalspikes, and allows a steady-state response where the difference betweenthe inverting and non-inverting U4Out1 and U4Out2 signals is about 100mV, for example, where operational amplifier 1108 has a gain of about40, for example.

The Block 9 large-signal detection/fast recovery circuit 1100 issituated in the EP system at a location to remove a large-signal voltageoffset. A person of ordinary skill in the art will appreciate that thelarge signal detection/fast recovery circuit 1100 could be locatedelsewhere in the EP system where potential large signal spikes may occurand are unwanted. A person of ordinary skill in the art will alsoappreciate that electronic components, such as the capacitors 1120,1124, 1128, 1132 and the resistors 1118, 1122, 1126, 1130 of the timingbanks 1158, can be substituted within the large signal detection/fastrecovery circuit 1100 to change circuit activation levels and times. Thelarge-signal detection/fast recovery circuit 1100 can be used in variousembodiments of other signal acquisition and processing systems to removea large-signal voltage offset from other types of electrical signals, aswould be appreciated by a personal of ordinary skill in the art.

In some embodiments, the outputs In14, In24 of the Block 9 large-signaldetection/fast recovery circuit 1100 (see FIG. 4, 418) are fed back intoBlock 4, the DC Block (see FIG. 4, 408 a and 408 b). The DC blockingcapacitors of Block 4 (not shown) add an additional bias (e.g., acorrecting bias) back to the input signals. Accordingly, a signal fromthe Block 9 large-signal detection/fast recovery circuit 1100 is not fedback into the Block 4 DC Block unless the signal fed into Block 9 islarge (e.g., with an amplitude on the order of 100 mV or greater). Inother words, the output signal of Block 9 does not pass into Block 4unless a large signal event occurs. Nodes In14 and In24 are normallydisconnected.

The exemplary embodiment of the large-signal detection/fast recoverycircuit 1100 of FIG. 11 is described in detail relative to the signalplots of FIGS. 12, 13A-13C, 14A-14D, and 15A-15B. A sample signal isapplied at the inputs to the EP system, and described at various pointsthrough the circuit. In this example, the signals shown to demonstratethe large-signal detection/fast recovery circuit 1100 are generated byapplying a 20 mVpp signal at node In12 of FIG. 6A and FIG. 7, and zeroinput at node In22 (the symmetric negative node, not shown),specifically, the inputs to the RF filter 702. At time 10 msec, a 200 mVstep is added to the signal at node In12. This becomes a 200 mVdifferential signal as it traverses through the EP system, which canmake the signal move out of the display range of most conventionalmonitoring devices. Such 200 mV signals should generally be removed sothat the signals can be viewed in an EP environment.

FIG. 12 illustrates what happens to such an input signal if thelarge-signal detection/fast recovery circuit 1100 is not connected.After the sample input 20 mVpp signal with an unwanted 200 mV step-upgets through the analog input protection/filtering stage 530,instrumentation amplifier 1001, and differential amplifier #1 1017 toreach the large-signal detection/fast recovery circuit 1100, if thelarge-signal detection/fast recovery circuit 1100 is not connected, theEP hardware system cannot recover quickly from the 200 mV step signal.Such slow recovery complicates the identification of cardiac signals.

Resistors 1002 and 1004, located before the instrumentation amplifier1001 of FIG. 10, pull the offset signals back to a ground leveleventually, but a time constant of about 2.7 seconds is produced by theproduct of the DC blocking capacitor (not shown) of Block 4 and resistor1002. This introduced delay is too long to recover an off-screen orsaturated signal. FIG. 12 illustrates that the signal on the input nodeIn14 moves down inappreciably in about 100 msec and only a fewmillivolts in about 400 msec (not shown). Such a large-transient signalwill likely have an adverse impact on the operation of the EP systemwithout the large-signal detection/fast recovery circuit 1100, becausethe large transient would push the monitored signal to saturation andthe waveform details of the signal would be lost.

FIGS. 13A-13C illustrate the same 200 mV large-transient signal whenusing a connected large-signal detection/fast recovery circuit 1100. Inthis example, as shown in FIGS. 13A and 13B, both input nodes of thelarge-signal detection/fast recovery circuit 1100, In14 and In24 (shownin FIG. 11), are pulled (biased) toward the common mode signal V(CMB),which is at an amplitude of about 100 mV (see FIG. 13C). In14, thepositive input node of the large-signal detection/fast recovery circuit1100, is pulled down, and In24, the negative input node of thelarge-signal detection/fast recovery circuit 1100, is pulled up. V(CMB)is the average of the voltage at nodes In14 and In22 (the symmetricnegative input to the overall circuit). The actual common mode level ofnodes In14 and In24 has no impact because the desired bias level isapplied directly to the differential amplifiers of Blocks 6 and 7 (1020and 1034, respectively), which sets the common mode voltage at thosedifferential amplifiers 1020, 1034.

The plots in FIGS. 13A and 13B illustrate that the voltages of nodesIn14 and In24 are pulled into monitoring range after about 50milliseconds. The limiting, or “soft clamping,” is thus performedgradually to avoid discontinuity in the signal acquisition andvisualization. Other embodiments may allow for a gradual “clamping” inabout 100 milliseconds.

FIGS. 14A-14D demonstrate how a large-transient signal is conditioned asit traverses the various internal nodes of the large-signaldetection/fast recovery circuit 1100. Signal plots V(A) of FIG. 14A andV(B) of FIG. 14B represent the outputs of the operational amplifier 1108of the large-signal detection/fast recovery circuit 1100 in FIG. 11. Inthis example, operational amplifier 1108 has a gain of about 40,relative to the input, and produces a (40×200 mV=) 8-volt differentialsignal across nodes A and B in FIG. 11.

As shown in plot V(C) of FIG. 14C, following node B of FIG. 11, thenegative signal pulls down the voltage at node C of FIG. 11. Here, thesignal has been filtered to remove the in-band signal that occurs atnode B, leaving a low-frequency control voltage at node C. The negativevoltage at node C is connected to In14 through resistor 1140, diode1150, and resistor 1144. This produces a current that pulls In14 downtoward the common mode voltage, such as illustrated in FIG. 13A.Similarly, as shown in plot V(E) of FIG. 14D, node A pulls up In24toward the common mode voltage through node E and J of FIG. 11.

The diodes in the large-signal detection/fast recovery circuit 1100 ofFIG. 11 control the direction of current flow. The first pair of diodestages 1114, 1116 (limiting diodes) allows different time constants forcharging and discharging nodes C, D, E, and F. They also provide anon-operating range where the nodes C, D, E, and F are not charged whenthe outputs A and B are less than the diode forward voltage drop. The“clamping” diodes 1150, 1152, 1154, 1156 of the second pair of diodestages 1146, 1148 ensure that input nodes In14 and In24 are pulled inthe correct direction.

FIGS. 15A-15B show signal plots of the current through the resistors1144, 1142 at the outputs In14 and In24, respectively, of thelarge-signal detection/fast recovery circuit 1100 of FIG. 11. Duringnormal operation, the current is 0 and the instrumentationamplifier/filter 410 circuit is unaffected. When the differential levelis too high (that is, when a large signal is detected, for example, inexcess of 100 mV over several milliseconds), the current in those tworesistors 1144, 1142 help pull the signals back toward the common modevoltage, V(CMB).

A/D Converter

The A/D Converter 416, Block 8 (see FIG. 4), is a fully differential A/Dconverter that is designed to accept differential signals from the restof the circuit. In some embodiments, each of the EP system circuitmodules is duplicated eight times so to feed as differential pairs intothe eight separate channels of the A/D Converter 416. A TI ADS 127824-bit, 8-channel delta-sigma converter can be used, for example. Aperson of ordinary skill in the art may choose other A/D converters ofsimilar specifications.

In some embodiments, the A/D converter 416 is highly linear, acharacteristic of delta-sigma converters. The high linearity allowsaccurate digital signal processing to be performed in the software, asdescribed below. This configuration minimizes hardware filtering to thatadvantageous for RF attenuation and anti-aliasing, and allows moreflexibility of filtering and signal processing in software. Theadvantage of choosing a fully differential A/D converter is that commonmode noise signals from any digital circuitry (e.g., a digital clocksignal) are rejected.

Wilson Central Terminal-Right Leg Drive (WCT-RLD) Circuit

Although input common mode signals can be at any frequency, the dominantsignals are generally at the power line frequency: 60 Hz in the U.S.,for example. In a conventional EP environment, ECG (and similar)equipment mitigates a large amount of 60 Hz noise that could be up to100 times larger than the signal of interest. In addition, because ofdistortions in the power line signal, there is often a strong thirdharmonic at 180 Hz, which is generally the noisiest harmonic. Higherharmonics and other common mode signals are generally smaller and/or areabove the frequency band of interest for the ECG and IC signals.

In some embodiments, a Wilson Central Terminal-Right Leg Drive (WCT-RLD)circuit is used to remove particularly the 60 Hz and 180 Hz noise bycommon mode rejection, that is, by enhancing the first and thirdharmonic frequencies of the power line signals and selectively feedingthose signals back to the patient to cancel them out. FIG. 23illustrates a schematic diagram of an improved WCT-RLD circuit,according to some embodiments.

For example, a WCT circuit 2332 of FIG. 23 provides a virtual ground bysumming and averaging two or three limb electrodes (e.g., right arm 2304and left arm 2306, or the right arm 2304, left arm 2306, and left leg2308) connected to a central terminal 2336 through two or three largeresistors 2334 (e.g., 20 kOhms on each electrode). A person of ordinaryskill in the art will understand that the average of the right arm (RA)2304, left arm (LA) 2306, and left leg 2308 provides a more accurateestimate of the common mode signal on the patient 2302 than does theaverage of the right arm (RA) 2304 and left arm (LA) 2306. As alsounderstood by a person of ordinary skill in the art, the RA and LAsignals are alternatively buffered (see buffer 2312) versions of the RLpositive (RLP) 2338 and RL negative (RLN) 2340 signals. A WCT isconventionally designed to reduce the overall 60 Hz common mode noisesignal by bringing the net potential difference of these limb leadsclose to zero.

The addition of an active current via the right leg, the “right legdrive” (RLD) circuit 2330, to the WCT circuit 2332 allows the patient tobe driven to the same voltage as the common amplifier, thus reducing thecommon mode voltage at the inputs of the ECG electrodes (LA, RA, LL, andV1 to V6). This can be done by generating the inverse of the common modesignal and applying that as an output to the right leg. Specifically,the right leg drive is represented by limb electrode RL. The patient2302 receives, through the RL electrode, an RLD output 2310, a summedand inverted version of the other IC catheter signals or ECG electrodesignals, canceling interference present in the patient's body. This, incombination with the common mode rejection properties of the signalamplification stage 532, can reduce common mode low-frequencyinterference to acceptable levels (specified by standard IEC 60601-2-25,for example).

However, because 60 Hz and 180 Hz noise is not equal in all parts of thebody, common mode rejection alone cannot remove all of the noise. TheWCT-RLD circuit 2300 of FIG. 23 provides a reference signal,approximately equal to the line frequency coming into the system, whichfurther reduces the overall common mode signal. Thus, the combination ofthe disclosed WCT-RLD circuit 2300 and conventional common moderejection provides an advantageous improvement in the reduction of thecommon mode signal.

In an exemplary embodiment using the WCT, the WCT input within the EPsystem can provide an optional unipolar input to replace the bipolarpositive (+) or negative (−) catheter input to the Block 3 Buffercircuit (see FIG. 4, 406 a and 406 b). Specifically, the WCT-RLD circuit2300 averages the right arm 2304, left arm 2306, and left leg 2308electrode signals. The result is buffered by the operational amplifier2314, and the output WCTBuf 2316 is sent as a unipolar feedback signalwherever it is desired in the EP system, specifically used inembodiments whenever a patient is connected. The WCT-RLD disclosedherein enhances a conventional unipolar WCT solution with a novelapproach for generating an RLD signal.

In some embodiments, a novel approach in the WCT-RLD circuit 2300 is toprovide additional filter circuitry, called a “Twin-T” feedback network2440 (see FIGS. 23 and 24), which can produce a stronger RLD at the 60Hz power line frequency or at the 180 Hz third harmonic frequency. Thisis specifically helpful during ablation. The Twin-T feedback network2440 resonates at both 60 Hz and 180 Hz, but advantageously preventsphase oscillations by reducing feedback at other frequencies.

FIG. 24 illustrates a schematic diagram of a Twin-T feedback network2440 interfaced with the RLD circuit 2330 of the WCT-RLD circuit 2300,according to some embodiments. The Twin-T feedback network 2440 of FIG.24 serves as an improved notch filter. Resistors 2406, 2407, 2408, 2409,2410, 2411, and capacitors 2401, 2402, 2403, 2404 form a single Twin-Tnetwork that generates a notch at 60 Hz. The next stage, resistors 2412,2413, 2414, 2417, 2418, 2419, and capacitors 2415, 2416, 2420, 2421,similarly generates a notch at 180 Hz. However, when the network is inan operational amplifier feedback path, the inverse function isobtained.

For example, as illustrated in the plot 2500 of FIG. 25, the RLD outputof the Twin-T feedback network 2440 at operational amplifier 2425produces two peaks, one at 60 Hz 2510 and one at 180 Hz 2520. At higherfrequencies, such as 10 kHz or greater, the phase change goes to zero.This prevents phase changes in the RLD circuit 2330 at these higherfrequencies that can cause oscillation. Minimal phase changes at thesehigher frequencies can prevent oscillations near the ablationfrequencies, which would otherwise be more difficult to filter out.

Although Twin-T circuitry is used in electronic design, it has not beenpreviously used in a WCT-RLD circuit as disclosed herein. The Twin-Tfeedback network 2440 removes power line signals conventionally passedby known circuits when generating a RLD signal, such that the power linesignals do not affect phase response at higher frequencies. The Twin-Tfeedback network 2440 thus has an advantageous use for generating a RLDsignal from electrode leads.

In the embodiment of FIG. 23, the RLD circuit 2330 follows the powerline by feeding the RLD output 2310 as a separate signal back into thepatient 2302. In the circuit, the right leg positive (+) (RLP) 2338 andright leg negative (−) (RLN) 2340 differential input signals, which canalternatively be the RA and LA signals, are buffered 2312. Then, theTwin-T feedback network 2440 emphasizes/amplifies the buffered right legsignal at 60 Hz and 180 Hz, which is inverted and buffered again by theRLD circuit 2330. This RLD circuit 2330 includes an operationalamplifier 2328, resistors 2320, 2324, 2326, and capacitors 2318, 2322.After passing through the RLD circuit 2330, the signal is output as theRLD output 2310 (RLDrv) at a surface lead on the patient's right leg.The effect is that the entire circuit tracks the power line, and thecommon mode of the circuit rejects the power line noise. Additionally,the circuit of the right leg drive protects against any signal goingback into the patient that is greater than approximately one (1)microampere.

The following cases illustrate how the disclosed hardware circuitryconditions signals found in an EP environment, allowing improved cardiacmonitoring in the midst of equipment and environment noise, and duringprocedures that introduce large, potentially interfering signals intothe monitoring environment.

Signal Case #1—Common Mode 60 Hz and in-Band 500 Hz Differential Signal

Signal case #1 presents a typical common mode 60 Hz noise signal with anin-band (less than 1000 Hz) differential signal as found fromconventional IC leads. In this example, a series of signal plotsrepresenting the signal at exemplary nodes of the disclosed circuit isshown. The circuit amplifies the differential signal and rejects thecommon mode signal.

FIGS. 17A-17B illustrate an input signal of 2 Vpp 60 Hz sine (powerline) signal applied to input nodes In12 (see FIG. 6A) and In22 (thenegative, lower branch of the circuit, not shown), respectively.Superimposed on In12 is a 0.2 Vpp, 500 Hz sine wave signal (see plotV(In12) of FIG. 17A) and on In22 is a −0.2 V, 500 Hz sine wave signal(see plot V(In22) of FIG. 17B). This results in a 2 Vpp, 60 Hz commonmode signal and a 0.4 V, 500 Hz differential signal. These signals maybe too low in frequency to be affected by the RF filter 702 of Block 2,so the same signals appear at the output of Block 3 (Buffer 406 a, 406b) and after Block 4 (DC Block 408 a, 408 b).

FIGS. 17C-17D illustrate shield input signals (Shield1, Shield2) thatare also the same as the corresponding input signals shown in FIGS.17A-17B. These signals are fed back from Block 10 (low-frequencyfeedback circuit 1600) to the RF filter 702 to eliminate loading fromthe RF filter 702. (See Shield1, 728 of FIG. 7. Shield2, the negative,lower branch of the circuit, is not shown.) The voltage change oncapacitors 714, 716, 706 of the upper branch of the RF filter 702 inFIG. 7, as well as on the corresponding capacitors on the symmetricallower branch of the RF filter (not shown) is close to 0, effectivelyremoving them from the circuit at low frequencies.

FIGS. 18A-18B illustrate Out1 and Out2, the outputs of Block 5(instrumentation amplifier 1001 of FIG. 10) with a differential gain of20. The common mode signal has a gain of 1 and the differential signalshave a gain of 20. The signal at this point becomes a 2 Vpp, 60 Hz sinewave at each output with a superimposed 4 Vpp, 500 Hz signal at Out1(see FIG. 18A) and a −4 Vpp, 500 Hz signal at Out2 (see FIG. 18B),creating a 8 Vpp differential signal.

FIGS. 18C-18D illustrate the outputs B2OutP and B2OutN of FIG. 10,respectively. At B2OutP and B2OutN, the signals have passed through thefully differential operational amplifiers (Blocks 6 and 7, 1017, 1021)of FIG. 10, have eliminated the common mode signal, and have referredthe outputs to the common-mode output voltage, VOCM (2.5V bias level).The gain of 0.5 at amplifier 1034 of Block 7 results in a final set of500 Hz signals of 2 Vpp at B2OutP (see FIG. 18C) and −2 Vpp at B2OutN(see FIG. 18D), which is equivalent to a 4 Vpp differential 500 Hzsignal. From the input to the output, the common mode gain is 0 and thedifferential gain is 10. The common mode signal can thus be eliminatedthrough the combined responses of the instrumentation amplifier (Block5) and the fully differential operational amplifiers (Blocks 6 and 7).

Signal Case #2—500 kHz Ablation Signal

Signal case #2 presents a typical 500 kHz ablation signal applied to theEP system inputs during an ablation procedure as cardiac monitoringcontinues. The unwanted ablation signal is filtered and attenuatedbefore reaching the A/D converter (see FIG. 4, Block 8, 416) of thedisclosed circuit.

As seen in FIGS. 19A-19B, the ablation signal input is a 0.2 Vpp, 500kHz sine wave applied to In12 (FIG. 19A) and −0.2 Vpp, 500 kHz sineapplied to In22 (FIG. 19B). This results in a 0.4 V, 500 kHzdifferential signal. This signal is in the frequency range to beattenuated by the RF filter 702 of Block 2 (FIG. 4, 404 a and 404 b).

FIGS. 19C-19D illustrate plots of the output of the RF filter 702 (Block2) In13 (and the symmetric lower branch RF filter output In23) when thecircuit receives an ablation signal. The plots V(In13) of FIG. 19C andV(In23) of FIG. 19D are shown at the same scale as the input. The signalcan be seen to be attenuated to a few millivolts.

The plots of V(Shield1) and V(Shield2) shown in FIGS. 20A and 20B,respectively, illustrate that the same signals over the shield input(see Shield1 of FIG. 7, for example) are also greatly attenuated,effectively grounding the lower plates of capacitors 714, 716, 706 ofthe upper branch of the RF filter 702 in FIG. 7, and the correspondingcapacitors on the symmetrical lower branch of the RF filter (not shown),to enable the RF filter to attenuate the 500 kHz ablation signal.

FIGS. 21A and 21B illustrate plots of the signals V(Out1) and V(Out2),respectively, at the outputs of the Block 5 (instrumentation amplifier1001 of FIG. 10), with a gain of 20. The remaining 500 kHz signal goesthrough this 20× gain stage, but the filtering on this stage (fromcapacitors 1010 and 1012) limits the gain at 500 kHz to approximately1×.

As shown in FIGS. 21C-21D, the successive fully differential operationalamplifiers 1017, 1021 in Blocks 6 and 7 of FIG. 10 (and their negative,lower branch circuit equivalents) continue to filter the 500 kHz signaluntil it is less than 0.5 mV at B2OutP (FIG. 21C) and B2OutN (FIG. 21D).The remaining signal is removed by the filter on the Block 8 A/Dconverter (see FIG. 4, 416), which provides 100 dB attenuation above1000 Hz. The ablation signal is thus eliminated through the combinedresponses of the RF filter (Block 2), the instrumentation amplifier(Block 5), and the fully differential operational amplifiers (Blocks 6and 7).

Hardware/Software Interface

FIG. 5A illustrates the relationship between the hardware and softwareof the disclosed EP recording system, according to some embodiments. TheMain System Unit (MSU) 504 contains the hardware circuitry of the EPrecording system. In FIG. 5A, the ECG board 506 with WCT 507 correspondsto the ECG board 302 and WCT 314 shown in FIG. 3. (For cross-reference,the ECG board 302, 506 digital signal outputs are V1-V6 310 and I-II312.) Similarly, the IC board 508 corresponds to the IC board 316 inFIG. 3. (For cross-reference, the IC board 316, 508 digital signaloutputs IC1 . . . ICN are ICUniWCT1-ICUniWCT2 326,ICUniINDIF1-ICUniINDIF2 328, and ICDiff1 . . . ICDiffN 330.) Tocommunicate the digital signal outputs from the ECG board 506 and ICboard 508 to the software of the Main Processing Unit (MPU) 514, aCommunication Module 510, and a fiber optic link 512 are provided.

According to some embodiments, the Communication Module 510 of the MSU504 transmits the independent digital signals from the A/D converter416, 534 of the ECG board 506 and IC board 508 to the MPU 514 over afiber optic link 512 for digital signal processing. The CommunicationModule 510 samples the output channels from the A/D converter 416, 534,converts them to serial format, and transmits the data over the fiberoptic link 512. The signals are converted back to a parallel format atthe receiving end of the fiber optic link 512 in the MPU 514.

In this specification, the ECG board 302, 506 and IC board 316, 508 arenamed thusly for sake of convenience. As would be understood by a personof ordinary skill in the art, the circuitry of the ECG board 302, 506and IC board 316, 508 can accept other physiologic signals from varioustypes of electrodes other than ECG and IC electrodes.

EP Recording System Software Description

Provided herein are system, apparatus, device, method and/or computerprogram product embodiments, and/or combinations and sub-combinationsthereof, for processing and displaying multiple signals in nearreal-time. For example, the embodiments may involve processing anddisplay multiple biomedical signals (e.g., EP signals) in nearreal-time. Before describing further details of these embodiments, abrief overview of digital signal processing is provided.

At a high level, digital signal processing is the use of digitalprocessing to identify particular features in a signal, or producing asignal that is of higher quality than the original signal (e.g., byremoving noise from the signal). Digital signal processing may beperformed on a digitized electrocardiography (ECG) or intracardiac (IC)signal representing the electrical activity of a heart over a period oftime.

To perform digital signal processing on an analog signal, the analogsignal needs to be converted to digital form. An analog-to-digital (AD)converter such as A/D converter 416 can convert the analog signal todigital form, as is well known to a person of ordinary skill in the art.

Digital signal processing may involve applying a digital signalprocessing function to one or more signal samples in a sequence ofsignal samples for a signal. A digital signal processing function can bea sequence of mathematical operations and computational algorithms. Adigital signal processing function can measure, filter, compress, oroptimize a signal sample, for example.

Digital signal processing can use different digital signal processingfunctions depending on the type of analysis and the type of signal beingprocessed. For example, digital signal processing can use a differentdigital signal processing function to identify particular words in aspeech signal or to remove motion blur from a video signal.

Digital signal processing systems have many applications such as audiosignal processing, audio compression, digital image processing, videocompression, speech processing, speech recognition, digitalcommunications, digital synthesizers, radar, sonar, financial signalprocessing, and seismology. But conventional digital signal processingsystems often cannot be used in certain applications such as biomedicalsignal processing. This is because conventional digital signalprocessing systems, including current EP solutions, are often unable tosimultaneously display multiple signals in near real-time. Moreover,conventional solutions do not enable a user to dynamically apply a newdigital signal processing function to a base signal. And, conventionalsolutions are often unable to synchronize the processing and display ofmultiple signals in near real-time. This is often problematic inclinical settings because the ability of a physician to make aneffective clinical diagnosis may depend on comparing multiple signals atthe same point in time. Finally, conventional EP systems that use analogfilters are often unable to take full advantage of digital signalprocessing. This is because when functions are implemented in hardware,the options are greatly restricted. For example, the functions cannot beremoved and therefore the full potential of digital signal processingcannot be obtained.

FIG. 26 is a block diagram of a system 2600 for processing anddisplaying multiple signals in near real-time, according to someembodiments. System 2600 can represent MPU (Software) 514 in FIG. 5A,and implement digital processing stage 528 of FIG. 5B. System 2600includes signal path module 2602, configuration path module 2620, andmonitoring module 2622. Signal path module 2602, configuration pathmodule 2620, and monitoring module 2622 can be software modules capableof being executed by a processor (or processors) such as processor 5004in FIG. 50. Alternatively, a plurality of processors can be used.

Signal path module 2602 includes input module 2604, timer 2605,packetizer 2606, queuing module 2608, packet dispatcher 2610, globalsignals table 2612, and output module 2616. Input module 2604, timer2605, packetizer 2606, queuing module 2608, packet dispatcher 2610,global signals table 2612, and output module 2616 can be softwaremodules capable of being executed by a processor (or processors) such asprocessor 5004. Signal path module 2602 solves at least thetechnological problem of how to synchronize the processing and displayof multiple signals in near real-time. Signal path module 2602 solvesthis technological problem using a novel multistage process involvingpacketization, queueing, and processing delay equalization, as describedbelow.

In a first stage, input module 2604 can receive signal samples for oneor more base signals. A base signal can be a signal before any digitalsignal processing is applied. For example, a base signal can be abiomedical signal such as an ECG or IC signal. As would be appreciatedby a person of ordinary skill in the art, a base signal can be variousother types of signals. Input module 2604 can receive signal samples formultiple base signals. For example, input module 2604 can receive signalsamples of an IC signal and signal samples of an ECG signal.

Input module 2604 can receive signal samples of a base signal from ahardware device associated with MSU (Hardware) 504 in FIG. 5. Forexample, input module 2604 can receive signal samples from a hardwaredevice such as EGG board 302 or IC board 316 in FIG. 3. Input module2604 can also receive signal samples from data stored in a computerfile. For example, the computer file can contain previously recordedsignal samples received from a hardware device.

Input module 2604 can receive signal samples from a hardware device viaA/D converter stage 534. For example, input module 2604 can receivesignal samples of a base signal from EGG board 302.

Input module 2604 can receive signal samples of a base signal from anelectrode attached to a hardware device. For example, input module 2604can receive signal samples for each of eight (8) electrodes attached toECG board 302. As would be appreciated by a person of ordinary skill inthe art, input module 2604 can receive more or fewer signal samplesdepending on the number of hardware devices connected to input module2604, and the number of electrodes attached to each hardware device.

Input module 2604 can store the one or more signal samples for each basesignal in a computer storage device for later analysis by review module2624. For example, input module 2604 can store the one or more signalsamples in main memory 5008 or hard disk drive 5012 in FIG. 50. Thisenables a user (e.g., a physician) to review the one or more signalsamples for each base signal after having been acquired.

Input module 2604 can dispatch the one or more signal samples for eachbase signal to packetizer 2606. Packetizer 2606 can performpreprocessing on the received signal samples. Packetizer 2606 canperform preprocessing on the received signal samples to ensure that theresulting signal is compatible with later stages in signal path module2602. As would be appreciated by a person of ordinary skill in the art,the type of preprocessing that packetizer 2606 performs can depend onthe type of base signal. For example, packetizer 2606 can convert thebinary values of the received signal samples to their correspondingphysical values, e.g., for display of the base signal.

After preprocessing the received signal samples, packetizer 2606 canstore the one or more signal samples of a base signal into a packet. Apacket may be a consecutive sequence of N signal samples belonging tothe same base signal. Packetizer 2606's storage of signal samples intopackets can enable signal path module 2602 to synchronize the processingand displaying of multiple signals in near real-time, especially on anon-real-time operating system. In other words, a packet is the unit ofprocessing in signal path module 2602.

Packetizer 2606 can store one or more signal samples in a packet basedon timer 2605. Timer 2605 can be a high-resolution timer. For example,timer 2605 can be a Microsoft Windows® high-resolution timer having a1-millisecond resolution. Timer 2605 can be set to an amount of timeassociated with receiving a fixed number of signal samples (e.g., Nsignal samples) from a hardware device or from a computer file. Thefixed number of signal samples may correspond to the number of signalsamples capable of being stored in a packet.

Packetizer 2606 can use timer 2605 to ensure that each packet containsthe same number of signal samples. Specifically, packetizer 2606 can settimer 2605 to an amount of time associated with receiving a given numberof signal samples of a base signal. In other words, packetizer 2606 canexpect to receive a certain number of signal samples when timer 2605 istriggered.

Packetizer 2606 can start timer 2605. Packetizer 2606 can then storesignal samples received from input module 2604 into a packet until timer2605 is triggered. Packetizer can then dispatch the packet to queuingmodule 2608. Packetizer 2606 can then restart timer 2605. Packetizer2606 can then store a new set of signal samples received from inputmodule 2604 into a new packet until timer 2605 is triggered again.

Packetizer 2606 can assign a tag to each packet. Packetizer 2606 canassign the same tag to each packet associated with a different basesignal for the same period of time. This assignment can enable signalpath module 2602 to synchronize the processing and displaying of packetsfor different base signals for the same period of time. The assigned tagmay be used by a display module 2618 to synchronize the output ofdifferent signals. In other words, the display module 2618 can work onthe same tag at any given time.

The assigned tag can correspond to the time period in which signalsamples in the corresponding packet were received. Specifically, the tagcan correspond to the sample number of the first signal sample in thecorresponding packet. For example, packetizer 2606 can store sixteen(16) signal samples in each packet. In this case, packetizer 2606 canstore the first set of signal samples in a packet with a tag of 0.Packetizer 2606 can store the second set of signal samples in a packetwith a tag of 15. Packetizer 2606 can store the subsequent sets ofsignal samples in packets with tags of 31, 47, 64, etc. As would beappreciated by a person of ordinary skill in the art, other tagassignment conventions can be employed.

After packetization, packetizer 2606 can store each generated packetassociated with a given base signal in queuing module 2608. Queueingmodule 2608 is shown in FIG. 27.

FIG. 27 is a block diagram of queuing module 2608 for the storage ofeach generated packet associated with a different base signal, accordingto some embodiments. Queueing module 2608 solves at least thetechnological problem of how to dynamically apply multiple differentdigital signal processing functions to the same base signal. Queueingmodule 2608 solves this technological problem by storing generatedpackets associated with each base signal in separate queues that can bedynamically processed by different signal modules 2614. FIG. 27 isdiscussed with reference to FIG. 26.

Queuing module 2608 includes one or more queues 2702. For example, inFIG. 27, queuing module 2608 includes queue 2702-1, queue 2702-2, andqueue 2702-N. Each queue 2702 can be associated with a given basesignal. Queue 2702 can be a queue data structure that stores items inthe order they are inserted. For example, the first item inserted intoqueue 2702 is the first item removed from queue 2702. In other words,queue 2702 is a first-in-first-out (FIFO) data structure. As would beappreciated by a person of ordinary skill in the art, queue 2702 can beimplemented using an array, linked list, or various other datastructure.

Packetizer 2606 can store each generated packet associated with a givenbase signal in a corresponding queue 2702. For example, packetizer 2606can store generated packets associated with an IC signal into queue2702-1, and generated packets associated with an ECG signal into queue2702-2.

Packetizer 2606 can store each packet in a queue 2702 in the ordergenerated. This can ensure that the signal samples in the generatedpackets are processed in the order they are received from the hardwaredevice or from the computer file.

Returning to FIG. 26, packet dispatcher 2610 can dispatch a generatedpacket from a queue 2702 in FIG. 27 to one or more signal modules 2614in global signals table 2612 for digital signal processing. Packetdispatcher 2610 solves at least the technological problem of how todynamically apply multiple different digital signal processing functionsto the same base signal. Packet dispatcher 2610 solves thistechnological problem by dynamically dispatching generated packetsassociated with each base signal to the appropriate one or more signalmodules 2614 for digital signal processing.

Packet dispatcher 2610 can continuously scan the one or more queues 2702in queuing module 2608. Each time packet dispatcher 2610 detects a newpacket available in a queue 2702 in queuing module 2608, packetdispatcher 2610 can remove the new packet from the queue 2702. Packetdispatcher 2610 can then dispatch the new packet to one or more signalmodules 2614 in global signal tables 2612 for digital signal processing.Packet dispatcher 2610 can dispatch the same packet to multiple signalmodules 2614 so that the base signal can be simultaneously processedusing different digital processing functions. Moreover, because packetdispatcher 2610 can dispatch packets from different queues 2702 todifferent signal modules 2614, different base signals can besimultaneously processed using different digital signal processingfunctions.

Packet dispatcher 2610 can dispatch a new packet from a queue 2702 toone or more signal modules 2614. Packet dispatcher 2610 can dispatch thenew packet to one or more signal modules 2614 using global signals table2612. Global signals table 2612 can be a fixed size array. Each elementof the array can be associated with a given base signal, and thus agiven a queue 2702. For example, if there are 100 base signals, globalsignals table 2612 can be a fixed size array of 100 elements. Moreover,for each element of the array, there can be one or more signal modules2614 designed to process the corresponding base signal. In someembodiments, each element of the array can be a fixed size array itself.Each element of this subarray can be associated with a given signalmodule 2614. For example, if there are 10 signal modules 2614, thissubarray can contain 10 elements. Thus, by way of example and notlimitation, global signals table 2612 can be a 100×10 array.

Packet dispatcher 2610 can dispatch the new packet to a signal module2614 by checking the corresponding element in the subarray associatedwith the base signal of the new packet. Specifically, packet dispatcher2610 can determine whether the corresponding element in the subarrayindicates that the signal module 2614 is assigned to the base signalassociated with the packet.

In some embodiments, global signals table 2612 can indicate whether agiven signal module 2614 is assigned to a given base signal by storing a‘0’ or ‘1’ at the corresponding element in the subarray associated withthe given signal module 2614. For example, global signals table 2612 canindicate that the given signal module 2614 is not assigned to the givenbase signal by storing a ‘0’ at the corresponding element in thesubarray. In some other embodiments, global signals table 2612 canindicate whether a given signal module 2614 is assigned to a given basesignal by storing a reference to the given signal module 2614 at thecorresponding element in the subarray. As would be appreciated by aperson of ordinary skill in the art, the reference can be a memorypointer, flag, handle, or other type of identifier.

Packet dispatcher 2610 can also dispatch the new packet to one or moresignal modules 2614 using a lookup table. The lookup table may map agiven queue 2702 to one or more signal modules 2614. Packet dispatcher2610 can dynamically determine which one or more signal modules 2614 areassociated with a given queue 2702 using the lookup table. Packetdispatcher 2610 can then dispatch the packet to the one or moredetermined signal modules 2614 for digital signal processing.

Before packet dispatcher 2610 can begin dispatching packets to one ormore signal modules 2614 for digital signal processing, configurationpath module 2620 can configure signal path module 2602. Configurationpath module 2620 can perform this configuration during initialization ofsystem 2600, or when a user applies a new configuration to signal pathmodule 2602. Configuration path module 2620 is shown in FIG. 28.

FIG. 28 is a block diagram of configuration path module 2620 forconfiguring signal path module 2602 to synchronize the processing anddisplay of multiple signals in near real-time, according to someembodiments. Configuration path module 2620 solves at least thetechnological problem of how to synchronize the processing and displayof multiple signals associated with one or more base signals in nearreal-time. Configuration path module 2620 solves this technologicalproblem by equalizing the processing delays of each signal module 2614such that each signal module 2614 completes processing of the samecorresponding packet at approximately the same time. FIG. 28 isdiscussed with reference to FIG. 26.

Configuration path module 2620 includes a signal configuration module2802, a signal factory module 2804, a digital signal processor (DSP)equalizer 2806, and a DSP factory module 2808. Configuration path module2620 is a software module capable of being executed by a processor (orprocessors) such as processor 5004. Configuration path module 2620controls the execution of signal factory module 2804, DSP equalizer2806, and DSP factory module 2808. Signal factory module 2804, DSPequalizer 2806, and DSP factory module 2808 can be software modulescapable of being executed by a processor (or processors) such asprocessor 5004.

During initialization of system 2600, or in response to a user applyinga new configuration to system 2600, configuration path module 2620 cangenerate and configure one or more signal modules 2614 in global signalstable 2612. In some embodiments, the execution of signal path module2602 and monitoring module 2622 can be paused during the execution ofconfiguration path module 2620.

Configuration path module 2620 includes signal configuration module2802. Signal configuration module 2802 can receive one or more signalprocessing specifications. A signal processing specification can be usedto generate and configure a signal module 2614. A signal processingspecification may specify a base signal to process, the lengths of inputand output packet queues for a signal module 2614, and a digital signalprocessing function to use to process the base signal. Signalconfiguration module 2802 can receive the one or more signal processingspecifications from a computer file. The file may contain one or moresignal processing specifications previously specified by a user. Signalconfiguration module 2802 can also receive a signal processingspecification via a graphical user interface (GUI) in which a usermanually enters the signal processing specification using a series ofcomputer mouse, touch, keyboard, and/or voice recognition data entrytechniques, as would be appreciated by a person of ordinary skill in theart.

In response to receiving one or more signal processing specifications,signal configuration module 2802 can forward the one or more signalprocessing specifications to signal factory module 2804. Signal factorymodule 2804 can generate a signal module 2614 based on a signalprocessing specification. For example, signal factory module 2804 cangenerate a signal module 2614 as shown in FIG. 29.

FIG. 29 is a block diagram of a signal module 2614 generated by signalfactory module 2804, according to some embodiments. Signal module 2614can generate a processed signal from a base signal. Signal module 2614includes an input packet queue 2902, a digital signal processor (DSP)2904, and an output packet queue 2906. FIG. 29 can be discussed withreference to FIGS. 26 and 28.

Signal module 2614 includes input packet queue 2902, DSP 2904, andoutput packet queue 2906. Signal factory module 2804 can generate inputpacket queue 2902, DSP 2904, and output packet queue 2906 based on asignal processing specification from signal configuration module 2802.Input packet queue 2902 can store one or more packets from packetdispatcher 2610 for processing by DSP 2904. Input packet queue 2902 canbe a queue data structure that stores items in the order that they areinserted. For example, the first item inserted into input packet queue2902 is the first item removed from input packet queue 2902. In otherwords, input packet queue 2902 can be a first-in-first-out (FIFO) datastructure. As would be appreciated by a person of ordinary skill in theart, input packet queue 2902 can be implemented using a linked list, anarray, or various other data structure.

Output packet queue 2906 can store one or more packets processed by DSP2904. Output packet queue 2906 can be a queue data structure that storesitems in the order that they are inserted. For example, the first iteminserted into output packet queue 2906 is the first item removed fromoutput packet queue 2906. In other words, output packet queue 2906 canbe a first-in-first-out (FIFO) data structure. As would be appreciatedby a person of ordinary skill in the art, output packet queue 2906 canbe implemented using a linked list, an array, or various other datastructure.

Signal factory module 2804 can generate DSP 2904 based on a signalprocessing specification from signal configuration module 2802.Specifically, signal factory module 2804 can request DSP factory module2808 to generate DSP 2904. DSP factory module 2808 can generate DSP 2904based on a digital signal processing function specified in the signalprocessing specification. DSP factory module 2808 can further generateDSP 2904 based on one or more signal processing parameters associatedwith a digital processing function. For example, DSP factory module 2808can generate DSP 2904 based on a low-pass filter function and a cutofffrequency specified in a signal processing specification.

A DSP 2904 is a software module capable of being executed by a processor(or processors) such as processor 5004 in FIG. 50. DSP 2904 can apply adigital processing function to one or more packets, and therefore one ormore signal samples. As would be appreciated by a person of ordinaryskill in the art, a digital processing function may be a mathematicalalgorithm that takes one or more signal samples as input, processesthem, and produces one or more potentially modified signal samples asoutput. A digital processing function may be implemented using one ormore mathematical operations such as a fast Fourier transform. As wouldbe appreciated by a person of ordinary skill in the art, DSP 2904 canapply various types of digital processing functions. For example, DSP2904 can apply a low-pass filter, a high-pass filter, a band-passfilter, a band-stop filter, a notch filter, a comb filter, an all-passfilter, or various other filters as would be appreciated by a person ofordinary skill in the art.

DSP 2904 can also apply a digital processing function that analyzes asignal for various characteristics. For example, DSP 2904 can apply adigital processing function that determines whether a noise anomaly orsignal pattern is present in a signal. DSP 2904 can also analyze asignal by detecting repeated patterns in the signal. This may involvecomparing the signal to a previously detected (or recorded orsynthesized) signal pattern.

For example, DSP 2904 can determine a late potential in a signal.Specifically, DSP 2904 can determine a noise anomaly followed bysubsequent noise anomalies occurring at the same time relative to amatched beat. Each subsequent noise anomaly at the same relativeposition can increase a confidence level that a late potential has beenlocated. A display module 2618 can then display an indication of thelate potential.

Similarly, DSP 2904 can determine an early activation in a signal.Specifically, DSP 2904 can determine an earliest sharp intracardiacsignal above a selected threshold occurring within a predeterminedsegment before a reference point of a matched beat. A display module2618 can then display an indication of the early activation.

DSP 2904 can detect a pattern in a signal using a correlation function.For example, DSP 2904 can detect a pattern using a mean absolutedeviation algorithm. As would be appreciated by a person of ordinaryskill in the art, DSP 2904 can use various other types of patternmatching algorithms.

DSP 2904 can detect a pattern based on various signal characteristics.For example, DSP 2904 can detect a pattern based on shape, amplitude,and time characteristics. As would be appreciated by a person ofordinary skill in the art, DSP 2904 can detect a pattern based onvarious other types of signal characteristics.

DSP 2904 can also include one or more signal processing parameters. Thesignal processing parameters may control how DSP 2904 applies itsdigital processing function. For example, DSP 2904 can include one ormore signal processing parameters that specify a threshold frequency oran amplitude for filtering. DSP 2904 can also include one or more signalprocessing parameters that specify a signal pattern to detect, or anoise threshold value.

DSP 2904 can apply its digital processing function to a packet in inputpacket queue 2902. In some embodiments, DSP 2904 can scan input packetqueue 2902 for a new packet to process. In some other embodiments, DSP2904 can get a notification that a new packet is available in inputpacket queue 2902. DSP 2904 can then retrieve the packet from inputpacket queue 2902.

DSP 2904 can apply its digital processing function to the retrievedpacket. In other words, DSP 2904 can apply its digital processingfunction to the one or more signal samples in the packet. DSP 2904 cancontrol how it applies its digital processing function to the one ormore signal samples in the packet based on its one or more signalprocessing parameters. After processing the packet, DSP 2904 can storethe packet in output packet queue 2906 for display by output module2616.

As discussed below, each DSP 2904 can have an associated processingdelay. The processing delay can represent the amount of time to completeprocessing of a packet by the digital processing function of DSP 2904.The processing delay can vary between different DSPs 2904. This variancein processing delay between different DSPs 2904 can cause the DSPs 2904to output packets for display at different times, as discussed below.

After signal factory module 2804 completes generating input packet queue2902, DSP 2904, output packet queue 2906, signal factory module 2804 canconnect the output of input packet queue 2902 to the input of DSP 2904,and the output of DSP 2904 to the input of output packet queue 2906.Once signal factory module 2804 completes the connection, DSP 2904 canreceive packets from input packet queue 2902 representing an unprocessedbase signal. DSP 2904 can then process the packets using its digitalprocessing function. DSP 2904 can output the processed packets to outputpacket queue 2906. Signal factory module 2804 can further configureinput packet queue 2902 to receive packets from the base signalspecified in the signal processing specification.

Once the signal module 2614 is created, signal factory module 2804 canadd it to global signals table 2612. As discussed above, global signalstable 2612 can be a fixed size array. Each element of the array can beassociated with a given base signal. Moreover, each element of the arraycan be a fixed size array itself. Each element of this subarray can beassociated with a given signal module 2614.

In some embodiments, signal factory module 2804 can add the createdsignal module 2614 to global signals table 2612 by adding a new arrayelement to each subarray associated with a base signal. This new arrayelement can correspond to the newly created signal module 2614. Forexample, if global signals table 2612 previously contained ten (10)signal modules 2614, the newly created signal module 2614 can be addedat element number 11 in each subarray, for example.

Once the created signal module 2614 is added to global signals table2612, a user (e.g., a physician) can assign the created signal module2614 to a given base signal. In some embodiments, global signals table2612 can indicate whether the created signal module 2614 is assigned toa given base signal by storing a ‘0’ or ‘1’ at the corresponding elementin the subarray associated with the created signal module 2614. In someother embodiments, global signals table 2612 can indicate whether thecreated signal module 2614 is assigned to a given base signal by storinga reference to the created signal module 2614 at the correspondingelement in the subarray.

Signal factory module 2804 can generate multiple signal modules 2614.Each signal module 2614 can have a DSP 2904 that applies a differentdigital signal processing function. As a result, each signal module 2614can generate a different processed version of the same base signal. Thiscan enable a user to analyze the same base signal in a variety of ways.A user may also want to analyze the time-aligned output of multipleversions of the same base signal. This can enable the user to comparedifferent versions of the same signal at the same point in time ordifferent points in time.

As noted above, conventional digital signal processing systems are oftenunable to synchronize the display of multiple processed signals in nearreal-time. This may be because different digital signal processingfunctions have different processing delays. For example, a current EPsystem may apply two different digital signal processing functions tothe same base signal. But a medical team may want to synchronize thedisplay of the two processed signals. For example, a medical team maywant to compare an IC signal and an ECG signal at the same point in timein order to determine a clinical diagnosis. In other words, the medicalteam may want to time-align the display of the first processed signalwith the display of the second processed signal in near real-time. Butthis may not be possible if the two different digital signal processingfunctions have different processing delays. This is because one of thedigital signal processing functions may complete processing of the basesignal more quickly than the other digital signal processing function.As a result, one processed signal may be displayed before the otherprocessed signal.

The processing delay associated with a digital processing function maydepend on the complexity of the function. For example, a digitalprocessing function that performs low-pass filtering on a signal may beless computationally-intensive and use minimal memory. As a result, sucha digital processing function may have a short processing delay. Incontrast, another digital processing function may analyze a signal forparticular signal characteristics. This type of digital processingfunction may be more computationally-intensive and use more memory, andtherefore have a longer processing delay.

Because of the different processing delays, one processed signal may bedisplayed before another processed signal. This synchronization gap maybecome greater over time. For example, this synchronization gap maybecome greater where multiple signals are being processed and displayedin near real-time. This is because the difference in processing delaybetween two digital signal processing functions may be propagated toeach new signal sample.

For example, a first digital signal processing function may have aprocessing delay of 10 milliseconds for a given base signal. A seconddigital signal processing function may have a processing delay of 20milliseconds for the same base signal. The first digital signalprocessing function may complete processing of a first signal sample ofthe base signal at 10 milliseconds, and the second digital signalprocessing function may complete processing of the same first signalsample at 20 milliseconds. Thus, the first signal sample processed bythe first digital signal processing function may be displayed at 10milliseconds, and the first signal sample processed by the seconddigital signal processing function may be displayed at 20 milliseconds.In other words, the first signal sample processed by the first digitalsignal processing function may be displayed 10 milliseconds before thefirst signal sample processed by the second digital signal processingfunction.

This synchronization gap may increase when the second signal sample isprocessed. For example, the second signal sample may be received forprocessing by the first digital signal processing function at time 10milliseconds, and the second signal sample may be received forprocessing by the second digital signal processing function at time 20milliseconds. As a result, the second signal sample processed by thefirst digital signal processing function may be displayed at 20milliseconds, and the second signal sample processed by the seconddigital signal processing function may be displayed at 40 milliseconds.In other words, the synchronization gap may increase by 10 millisecondsfor the second signal sample; initially the synchronization gap is 10milliseconds and subsequently the synchronization gap is 20milliseconds.

This synchronization gap may increase where the digital signalprocessing is performed on a non-real-time operating system. Unlike anon-real-time operating system, a real-time operating system is a timebound system with well-defined fixed time constraints. A real-timeoperating system can guarantee that an application task is accepted andcompleted in a certain amount of time. In other words, a real-timeoperating system may provide a level of consistency concerning theamount of time it takes to complete a task.

In contrast, a non-real-time operating system cannot provide anyguarantee that an application task is completed in a certain amount oftime. For example, a non-real-time operating system may not provide aguarantee that the execution of a particular digital signal processingfunction is completed in a certain amount of time. As a result, theremay be a high degree of variability concerning the amount of time ittakes to complete a task. This may be problematic when attempting tosynchronize the processing and display of multiple processed signals.This is because a processing delay associated with a digital processingfunction may vary with each execution. For example, a digital signalprocessing function may normally complete execution in 10 milliseconds.But on a non-real-time operating system, there may be no guarantee thatthe digital signal processing function completes execution after 10milliseconds. For example, the digital signal processing function maycomplete execution in 30 milliseconds. This variability in processingdelay may further increase the synchronization gap.

In some embodiments, this display synchronization problem is solved in amultipronged way using an input packet queue 2902 and an output packetqueue 2906 of a signal module 2614, storing signal samples in a packetalong with an associated tag, and equalizing the processing delays amongone or more DSPs 2904.

An input packet queue 2902 and an output packet queue 2906 can solve thedisplay synchronization problem in three ways. First, they ensurepackets, and therefore signal samples, are processed and displayedsequentially. Second, an output packet queue 2906 can synchronize thedisplay of packets at the same point in time by blocking the processingof more packets until existing packets are consumed by output module2616. In other words, an output packet queue 2906 can provide a feedbackmechanism to a DSP 2904 that indicates when the DSP 2904 can stopprocessing more packets. Finally, an input packet queue 2902 ensures aDSP 2904 has packets to process. For example, when an input packet queue2902 is empty, a DSP 2904 can stop processing more packets. In otherwords, an input packet queue 2902 can provide a feedback mechanism to aDSP 2904 to indicate that there are no more packets to process.

DSP delay equalizer 2806 can also solve the display synchronizationproblem by equalizing processing delays across one or more DSPs 2904. Asdiscussed above, different digital signal processing functions havedifferent processing delays, which may cause the processed signals to bedisplayed out of sync. Therefore, if configuration path module 2620generates multiple signal modules 2614, each with a DSP 2904 having adifferent digital signal processing function, each signal module 2614can complete processing of a packet with a different processing delay.Because of these different processing delays, the processed signals maybe displayed out of sync by output module 2616. DSP delay equalizer 2806can solve this problem by equalizing the processing delays across thegenerated signal modules 2614.

In some embodiments, after configuration path module 2620 generates theone or more signal modules 2614, signal factory module 2804 can use DSPdelay equalizer 2806 to equalize the processing delays of each generatedsignal module 2614 such that each signal module 2614 outputs a processedpacket to its output packet queue 2906 at the same time. For example,DSP delay equalizer 2806 can determine the relative processing delaybetween two signal modules 2614. DSP delay equalizer 2806 can then usethe determined relative delay to configure a DSP 2904 in the firstsignal module 2614 to complete processing of a packet at approximatelythe same time as a DSP 2904 in the second signal module 2614 is designedto complete processing of a packet.

In some embodiments, DSP delay equalizer 2806 can perform theequalization by scanning each generated signal module 2614. During thescan, DSP delay equalizer 2806 can request the processing delayassociated with a DSP 2904 in each signal module 2614. DSP delayequalizer 2806 can request the processing delay using an applicationprogramming interface (API) of each signal module 2614. In response,each signal module 2614 can return its associated processing delay.

A signal module 2614 can store the processing delay associated with itsDSP 2904. The processing delay may be a predefined value specified inthe signal processing specification used to generate DSP 2904. In someother embodiments, DSP factory module 2808 can calculate the processingdelay of a DSP 2904 based on various factors including the digitalprocessing function used by the DSP 2904, the chosen signal processingparameters, and hardware characteristics such as the speed of theprocessor such as processor 5004, the size of the memory, and I/Olatency.

After determining the processing delay associated with a DSP 2904 ineach signal module 2614, DSP delay equalizer 2806 can determine themaximum processing delay among the signal modules 2614. For example, DSPdelay equalizer 2806 can determine that signal module 2614-1 has aprocessing delay of 10 milliseconds, that signal module 2614-2 has aprocessing delay of 20 milliseconds, and that signal module 2614-N has aprocessing delay of 50 milliseconds. Based on this, DSP delay equalizer2806 can determine that the maximum processing delay among the signalmodules 2614 is 50 milliseconds.

After determining the maximum processing delay, DSP delay equalizer 2806can configure the DSP 2904 of each signal module 2614 to have themaximum processing delay. For example, DSP delay equalizer 2806 can setthe processing delay of the DSP 2904 of each signal module 2614 using anAPI. In response, each DSP 2904 can be designed to process a packetusing its digital processing function and output the processed packet toits associated output packet queue 2906 at the end of the maximumprocessing delay. For example, in some embodiments, DSP 2904 can blockits output to its output packet queue 2906 if it completes processing apacket prior to the end of the maximum processing delay. In some otherembodiments, DSP 2904 can insert idle compute cycles during processingof a packet. As would be appreciated by a person of ordinary skill inthe art, various other approaches may be used to cause DSP 2904 tooutput a processed packet to its output packet queue 2906 at the end ofthe maximum processing delay.

Packetization and the assignment of tags to packets can solve thedisplay synchronization problem. As discussed above, each generatedpacket may include a fixed number of signal samples. Each packet mayalso include a tag indicating the packet's relative position among asequence of packets. In order to synchronize the display of multiplesignals, a display module 2618 can display packets having the same tag.In other words, the display module 2618 can synchronize its displayusing a tag.

As shown in FIG. 26, output module 2616 can include one or more displaymodules 2618-1 through 2618-N and review module 2624. Review module 2624can be a software module capable of being executed by a processor (orprocessors) such as processor 5004. Review module 2624 can display oneor more signals processed by one or more signal modules 2614 at aprevious point in time. The display modules 2618 can each be softwaremodules capable of being executed by a processor (or processors) such asprocessor 5004. A display module 2618 can display one or more livesignals processed by one or more signal modules 2614. Each displaymodule 2618 can operate independently of the other display modules 2618.In other words, each display module 2618 can simultaneously display oneor more signals on one or more display devices such as an input/outputdevice 5003 in FIG. 50. In some embodiments, each display module 2618can display its associated one or more signals in a particular GUIwindow on a given display device.

Each display module 2618 can display one or more signals. Each displaymodule 2618 can receive a packet from an associated output packet queue2906 in a signal module 2614 in global signals table 2612. Displaymodule 2618 can display a signal based on the packet.

FIG. 30 is a block diagram of a display module 2618, according to someembodiments. Display module 2618 includes a local signal table 3002, apacket index 3004, and display settings 3006. FIG. 30 is discussed withreference to FIG. 29.

As discussed, a display module 2618 can receive a packet from anassociated output packet queue 2906 in a signal module 2614. To receivethe packet, display module 2618 can maintain a reference to theassociated output packet queue 2906 in the signal module 2614. When adisplay module 2618 is designed to display multiple signals, the displaymodule 2618 can maintain references to the output packet queues 2906associated with each signal being displayed. The display module 2618 canstore the references in its local signal table 3002. Local signal table3002 can contain a list of one or more references to the output packetqueues 2906 associated with each signal being displayed. The displaymodule 2618 can remove a reference from its local signal table 3002 whenthe associated signal module 2614 is no longer active.

In some embodiments, a display module 2618 can continuously scan its oneor more associated output packet queues 2906 for new packets. Where thedisplay module 2618 is associated with a single output packet queue2906, each time the display module 2618 detects a new packet, it maydisplay the packet on a display device. However, where the displaymodule 2618 is associated with multiple output packet queues 2906, thedisplay module 2618 may not immediately display a new packet detected ina particular output packet queue 2906. This is because display module2618 can be designed to synchronize the display of multiple signals.

In some embodiments, where a given display module 2618 is designed tosynchronize the display of multiple signals, the display module 2618 candetect a new packet in a particular output packet queue 2906. Thedisplay module 2618 can then determine the tag associated with the newpacket. The display module 2618 can use this determined tag tosynchronize the display of new packets from the other output packetqueues 2906. For example, display module 2618 can wait to display anypackets to the display device until after detecting new packets at theother output packet queues 2906 that have the same determined tag. Oncedisplay module 2618 detects new packets having the same tag at its otherassociated output packet queues 2906, the display module 2618 cansimultaneously display the packets from its associated output packetqueues 2906. The display module 2618 can display the multiple signals ina non-overlapping stackable format. Because the display module 2618 candisplay packets having the same tag, the resulting displayed signals maybe time-aligned.

A display module 2618 can maintain the current active tag to display inpacket index 3004. Upon detecting a new packet in a particular outputpacket queue 2906, the display module 2618 can determine the tag of thenew packet. Display module 2618 can then set packet index 3004 to thedetermined tag.

A display module 2618 can include display settings 3006. Displaysettings 3006 can include one or more parameters that control howdisplay module 2618 displays its one or more associated signals. Displaysettings 3006 can specify colors to display the one or more associatedsignals. Display settings 3006 can specify a view format such as awaterfall view, dynamic view, or triggered view as discussed below.Display settings 3006 can specify a sweep speed for the one or moresignals. Display settings 3006 can contain various other types ofdisplay settings as would be appreciated by a person of ordinary skillin the art. Display settings 3006 can be designed by a user as discussedbelow.

Review module 2624 can display one or more signals processed by one ormore signal modules 2614 at a previous point in time. This can enable auser (e.g., a physician) to analyze the one or more signals long afterthey have been generated and displayed. In some embodiments, reviewmodule 2624 can capture a display of one or more signals in a displaymodule 2618 in response to a command. For example, a user can click abutton in a GUI to capture the current display of a display module 2618.The captured display can include the previously displayed visualizationof the one or more signals at the time of capture. In some embodiments,the display module 2618 can pause its display of new packets in responseto the capture of its current display.

In some embodiments, review module 2624 can capture the display of theone or more signals in the display module 2618 by determining a captureconfiguration of the display module 2618. The capture configuration caninclude the one or more active signals modules 2614 for the displaymodule 2618, the capture time, the selected view for the display module2618, the color scheme for the one or more displayed signals, andvarious other settings as would be appreciated by a person of ordinaryskill in the art. After determining the capture configuration, reviewmodule 2624 can apply the capture configuration to previously storedsignal samples.

As discussed above, input module 2604 can store one or more signalsamples for each base signal in a storage for later analysis by reviewmodule 2624. Review module 2624 can capture a display of the one or moresignals in the display module 2618 by applying the determined captureconfiguration to these stored signal samples. Specifically, reviewmodule 2624 can select the stored signal samples at the capture time inthe capture configuration. Review module 2624 can then process theselected signal samples using the active signal modules 2614 in thecapture configuration. Review module 2624 can also display the selectedsignal samples using the selected view, the color scheme, and variousother settings in the capture configuration. Thus, review module 2624can enable a user to review one or more processed signals for a displaymodule 2618 at a particular point in time, and subject to a particularconfiguration.

In some embodiments, review module 2624 can enable a user to change thereviewed interval for a display module 2618. For example, the user can“rewind” to a different point in time in the past (e.g., 5 minutes ago).After the capture time is changed, review module 2624 can display theone or more processed signals for the display module 2618 at the newreview time index.

FIG. 31 is a block diagram of monitoring module 2622, according to someembodiments. Monitoring module 2622 includes queue monitor 3102 andreport module 3104. Queue monitor 3102 and report module 3104 can besoftware modules capable of being executed by a processor (orprocessors) such as processor 5004.

Monitoring module 2622 can be continuously executed while signal pathmodule 2602 is being executed. For example, monitoring module 2622 canbe executed as a separate thread of execution by a processor. Monitoringmodule 2622 can determine whether there are issues in the execution ofsignal path module 2602.

In some embodiments, queue monitor 3102 can periodically scan queues inthe signal path module 2602. For example, queue monitor 3102 can scanthe queues 2702 in queuing module 2608. Queue monitor 3102 can also scanthe input packet queues 2902 and the output packet queues 2906 in theone or more signal modules 2614. Queue monitor 3102 can determine thestatus of each queue during the scan. For example, queue monitor 3102can determine the length of each queue during the scan. In someembodiments, if queue monitor 3102 determines a queue has an errorstatus, queue monitor 3102 can request report module 3104 to display theerror status on a display device. For example, queue monitor 3102 candetermine that a queue's length is continuously increasing. In response,queue monitor 3102 can request report module 3104 to display an errorthat indicates that the particular queue has an incorrect length.

FIG. 32 illustrates an example adjustment of a sweep speed for a displaymodule 2618, according to some embodiments. FIG. 32 includes a liveviewing area 3202 and a sweep speed 3204. FIG. 32 is discussed withreference to FIG. 26.

Live viewing area 3202 can contain the near real-time display of adisplay module 2618. In FIG. 32, live viewing area 3202 includes thenear real-time display of fourteen (14) different signals (e.g.,processed or base signals).

Sweep speed 3204 can be a GUI widget that allows a user to select asweep speed for live viewing area 3202. A sweep speed may represent atime scale of one or more signals displayed in live viewing area 3202.For example, the sweep speed may range from 10 mm per second to 1000 mmper second. In FIG. 32, sweep speed 3204 is shown being selected to be50 mm per second. As would be appreciated by a person of ordinary skillin the art, the choice of sweep speed may influence the level ofdisplayed detail, and therefore may be set based on the size of thedisplay screen.

FIG. 33 illustrates signal management for a display module 2618,according to some embodiments. FIG. 33 includes a signal managementwindow 3302. FIG. 33 is discussed with reference to FIG. 26.

Signal management window 3302 can include available signals 3304 andsignal settings 3306. Available signals 3304 can contain one or moresignals that can be selected for display by a display module 2618. Forexample, in FIG. 33, available signals 3304 contain fourteen (14)signals that can be selected for display by a display module 2618.Available signals 3304 can display various information about eachsignal. For example, available signals 3304 can display the name of thesignal and whether the signal is processed by a particular signal module2614.

Signal settings 3306 can display various settings that can be set foreach signal. For example, in FIG. 33, signal settings 3306 enables auser to change the name of each signal or assign each signal aparticular color. These settings may be stored in display settings 3006in display module 2618. Signal settings 3306 can also enable a user tochange various processing parameters associated with each signal. Theseprocessing parameters may be stored in the one or more signal processingparameters of a DSP 2904 of a signal module 2614 associated with thegiven signal.

FIG. 34 illustrates an example adjustment of zoom and clip factors for adisplay module 2618, according to some embodiments. FIG. 34 includes alive viewing area 3402 and a display settings window 3404. FIG. 34 isdiscussed with reference to FIG. 26.

Live viewing area 3402 can contain the near real-time display of adisplay module 2618. In FIG. 34, live viewing area 3402 includes thenear real-time display of fourteen (14) different signals (e.g.,processed or base signals).

Display settings window 3404 can include a zoom factor 3406 and a clipfactor 3408. Zoom factor 3406 can be a GUI widget to select a zoomfactor for a particular signal in live viewing area 3402. The selectedzoom factor can increase or decrease the size of the particular signal.For example, zoom factor 3406 can increase the size of a particularsignal from 0.02 to times 40.

Clip factor 3408 can be a GUI widget permitting a user to select a clipfactor for a particular signal in live viewing area 3402. The selectedclip factor can control how much a signal overshoots across the displayscreen. For example, a user can adjust the clip factor to reduce theactual area of where the particular signal is displayed so that if theparticular signal is large, it does not extend beyond the whole displayscreen so as to be partially unviewable.

FIG. 35 illustrates pattern searching for a display module 2618,according to some embodiments. FIG. 35 includes a live viewing area 3502and a pattern search window 3504. FIG. 35 is discussed with reference toFIG. 26.

Live viewing area 3502 can contain the near real-time display of adisplay module 2618. Pattern search window 3504 can be a GUI window thatenables a user to load or specify a signal pattern to search. Forexample, in FIG. 35, a user may create or load a search for a latepotential or early activation in one or more signals. The user may alsospecify various parameters for the search such as a search interval,beat detection confidence percentage, detection confidence percentage,or other parameters as would be appreciated by a person of ordinaryskill in the art. The signal pattern to search for may be stored in theone or more signal processing parameters of a DSP 2904 of a signalmodule 2614 associated with the given signal.

FIG. 36 illustrates a late potential search of a display of a displaymodule 2618, according to some embodiments. FIG. 36 includes a liveviewing area 3602. FIG. 36 is discussed with reference to FIG. 26.

Live viewing area 3602 can contain the near real-time display of adisplay module 2618 subject to a late potential search. A user maycreate or load the search for the late potential as previouslyillustrated in FIG. 35. Once a search is initiated, live viewing area3602 can display late potentials found in one or more signals. Liveviewing area 3602 can display the found late potentials with a detectionconfidence percentage. For example, in FIG. 36, found late potential3604 is shown with an 83% detection confidence. Live viewing area 3602can also display a tally of the total late potentials found.

FIG. 37A illustrates using a waterfall view for a display of a displaymodule 2618, according to some embodiments. FIG. 37A includes a liveviewing area 3702. FIG. 37A is discussed with reference to FIG. 26.

Live viewing area 3702 can contain the near real-time display of adisplay module 2618. Live viewing area 3702 can use a waterfall view todisplay the near real-time display of a display module 2618. Inwaterfall view, signals can be displayed side by side and verticallystacked on top of each other as a pattern is matched. Specifically, auser can select a pattern to match in a first signal (e.g., a specificbeat pattern). When the pattern is detected in the first signal, displaymodule 2618 can display a portion of the first signal that matches thepattern next to the corresponding portion of a second signal (e.g., anIC signal). The user can select the size of the portion of the firstsignal and the size of the portion of the second signal to be displayed.For example, the user can select the size of the portion of the firstsignal using a time interval (e.g., 150 milliseconds).

In waterfall view, each time the pattern is detected in the firstsignal, display module 2618 can vertically display each new portion ofthe first signal that matches the pattern along with the correspondingportion of the second signal. In other words, in waterfall view, displaymodule 2618 can display signals along a vertical time axis.

In FIG. 37A, live viewing area 3702 illustrates the near real-timedisplay of two different signals (e.g., V2[P1] and AB1.d) in a waterfallview. In FIG. 37A, signals V2[P1] and AB1.d are displayed side by sidestacked on top of each other. For example, at around time 10 seconds,signal portion 3704 is displayed side by side with signal portion 3706.Signal portion 3704 can represent a portion of signal V2[P1] thatmatches a given pattern (e.g., beat P1, lead V2) at around time 10seconds. Signal portion 3706 can represent the corresponding portion ofsignal AB1.d at the time the given pattern matched signal V2[P1].

A user (e.g., a physician) can find waterfall view advantageous. First,waterfall view enables a user to compare corresponding portions of twosignals side by side. Second, waterfall view can display signals on adisplay screen longer because the signals are vertically stacked. Incontrast, when signals are displayed left to right, it is oftendifficult for a user to analyze the signals because they are no longerdisplayed on the display screen after a short period of time.

FIG. 37B illustrates using a waterfall view via display module 2618,according to some embodiments. FIG. 37B includes a live viewing area3708 and a waterfall view 3710. FIG. 37B is discussed with reference toFIG. 26.

In FIG. 37B, live viewing area 3708 illustrates the near real-timedisplay of two different signals (e.g., V2[P1] and AB1.d). Waterfallview 3710 illustrates the near real-time display of the same twosignals, except signals V2[P1] and AB1.d are displayed side by side soas to appear stacked on top of each other. In waterfall view 3710, eachtime a signal pattern in a signal is detected, display module 2618 canvertically display the portion of the signal that matches the signalpattern along with the corresponding portion of a second signal.

For example, in FIG. 37B, signal portion 3712 of signal V2[P1] containsa signal pattern. Corresponding signal portion 3714 of signal AB1.dcorresponds to signal portion 3712 at the time of detection. In FIG.37B, waterfall view 3710 displays signal portion 3712 and correspondingsignal portion 3714 side by side (e.g., together) each time the signalpattern is detected in signal V2[P1]. In FIG. 37B, waterfall view 3710displays a portion of signal V2[P 1] that matches the signal patternalong with a corresponding portion of signal AB1.d from oldest tonewest. In other words, in FIG. 37B, waterfall view 3710 displays beatsthat scroll up in time with the oldest beats at the top and the newestbeats at the bottom. As would be appreciated by a person of ordinaryskill in the art, waterfall view 3710 can display the beats in variousother ways such as newest beats at the top and oldest beats at thebottom.

FIG. 37C illustrates using a dynamic view for a display of a displaymodule 2618, according to some embodiments. FIG. 37C includes a liveviewing area 3716. FIG. 37C is discussed with reference to FIG. 26.

Live viewing area 3716 can contain the near real-time display of adisplay module 2618. Live viewing area 3716 can use a dynamic view todisplay the near real-time display of a display module 2618. In dynamicview, a user can select a trigger for a signal (e.g., a correlation witha stored beat). The user can select the trigger from a plurality oftrigger types. A trigger type can be a signal characteristic of interestthat is associated with a secondary event of interest. When the triggeroccurs, display module 2618 can dynamically adjust the offset of thesignal so that it is pinned to a baseline. This can prevent the signalfrom progressing off the display screen. This is often important inclinical settings where the height of a signal peak can indicate aparticular type of injury, and a signal plateau can indicate theeffectiveness of an ablation lesion, for example.

In FIG. 37C, live viewing area 3716 illustrates a reference beatmeasured on a unipolar signal (e.g., Uni1) at a reference time (e.g.,reference time 3724). For example, this can occur during ablation. InFIG. 37C, signal 3718 can be the initial beat, signal 3720 can be thecurrent beat, and signal 3722 can be the maximum recorded beat sincesignal Uni1 was captured at reference time 3724. As discussed, indynamic view, a user can specify a reference location that determines apoint in a signal that is pinned to a baseline. In FIG. 37C, this pointis at pinned location 3726 (e.g., 0.0 mV) on the screen for signal Uni1.This can cause signal Uni1 to be offset so that it is pinned at pinnedlocation 3726.

FIG. 37D illustrates using a trigger view via a display module 2618,according to some embodiments. FIG. 37D includes a live viewing area3728 and a trigger view 3730. FIG. 37D is discussed with reference toFIG. 26.

Live viewing area 3728 can contain the near real-time display of adisplay module 2618. In FIG. 37D, trigger view 3730 illustrates thedisplay of live viewing area 3728 using a trigger view. In trigger view3730, a user can select a first signal (e.g., pacing signal 3732) thattriggers the display of other signals (e.g., II signal 3734, Uni Distsignal 3736, and Uni Prox signal 3738). The user can select a particulartrigger for the first signal. The user can select the trigger from aplurality of trigger types. A trigger type can be a signalcharacteristic of interest that is associated with a secondary event ofinterest. For example, the user can select a particular voltage (e.g.,60 millivolts) for the first signal. A person of ordinary skill in theart would understand that other signal characteristics can be selected.When the trigger occurs, display module 2618 can display the specifiedone or more signals synchronized in time and stacked vertically in thedisplay. A user (e.g., physician) can find trigger view advantageous.This is because it can enable the user to more easily view events thathappen relative to an event (e.g., start of pacing signal 3732).

In trigger view 3730, a user can also specify a time after the triggeroccurs where data is pinned to the baseline. For example, in FIG. 37D,the user sets the time to approximately 70 ms after the trigger occurs.In FIG. 37D, in response to user setting the time to approximately 70 msafter the trigger occurs, Uni Dist signal 3736 and Uni Prox signal 3738are pinned and always in view in trigger view 3730. In contrast, in FIG.37D, Uni Dist signal 3736 and Uni Prox signal 3738 are not in view inlive viewing area 3728 because they are not pinned to a baseline.

FIG. 38 illustrates the capture of a display of a display module 2618,according to some embodiments. FIG. 38 includes a live viewing area 3802and a review window 3804. FIG. 38 is discussed with reference to FIG.26.

Live viewing area 3802 can contain the near real-time display of adisplay module 2618. Review window 3804 can contain a previous displayshown in live viewing area 3802. To capture the display of live viewingarea 3802, a user may submit a capture request. For example, in FIG. 38,a user may click Review Button 3806. In response, review module 2624 candetermine a capture configuration of the display module 2618. Thecapture configuration can include the one or more active signals modules2614 for the display module 2618, a capture time, a selected view forthe display module 2618, a color scheme for the one or more displayedsignals, and various other settings as would be appreciated by a personof ordinary skill in the art. After determining the captureconfiguration, review module 2624 can apply the capture configuration topreviously stored signal samples and display the output in review window3802.

FIG. 39 illustrates the visual analyzation of a captured display of adisplay module 2618, according to some embodiments. FIG. 39 includes alive viewing area 3902 and a review window 3904. FIG. 39 is discussedwith reference to FIG. 26.

Live viewing area 3902 can contain the near real-time display of adisplay module 2618. Review window 3904 can contain apreviously-captured display shown in live viewing area 3802. A user mayanalyze the previously-captured output in review window 3904 usingvertical and horizontal calipers. Horizontal calipers can be a GUIselection widget. A user can use horizontal calipers to measureamplitude in millivolts (mV) for a particular signal. For example, asshown in FIG. 39, a user can click at the top and bottom of the V1signal to generate two horizontal lines (e.g., caliper lines 3908 and3910). The user may then hover the cursor along the V1 signal to displaythe measured amplitude at a particular point in time (e.g., measurement3906). Similarly, vertical calipers can also be a GUI selection widget.A user can use vertical calipers to measure time in milliseconds, orbeats per minute. A user can click at a left point and right point alonga signal to generate two vertical lines and display the measured time,or beats per minute, between the two vertical lines.

The following method descriptions for processing and displaying multiplesignals in near-real time are provided for embodiments related to ECGand IC signal visualization. A person of ordinary skill in the art wouldunderstand that these methods can apply equally to visualization ofother small physiologic signals.

FIG. 40 is a flowchart for a method 4000 for processing and displayingmultiple signals in near real-time, according to some embodiments.

Method 4000 shall be described with reference to FIG. 26. However,method 4000 is not limited to that example embodiment.

In 4002, configuration path module 2620 configures one or more signalmodules 2614. 4002 can be performed by method 4100 in FIG. 41.

In 4004, input module 2604 receives one or more signal samples for oneor more signals. For example, input module 2604 can receive one or moresignal samples for an IC signal, and one or more signal samples for anECG signal. 4004 can be performed by method 4400 in FIG. 44.

In 4006, input module 2604 dispatches the one or more signal samples topacketizer 2606.

In 4008, packetizer 2606 converts the one or more signal samples to oneor more packets. 4008 can be performed by method 4500 in FIG. 45.

In 4010, packetizer 2606 dispatches the one or more packets to queuingmodule 2608. 4010 can be performed by method 4600 in FIG. 46.

In 4012, packet dispatcher 2610 dispatches a packet from queuing module2608 to a signal module 2614 associated with the packet. 4012 can beperformed by method 4700 in FIG. 47.

In 4014, the signal module 2614 of 4012 processes the packet using a DSP2904. 4014 can be performed by method 4800 in FIG. 48.

In 4016, a display module 2618 associated with the signal module 2614 of4012 displays the processed packet to a display screen. 4016 can beperformed by method 4900 in FIG. 49.

FIG. 41 is a flowchart for a method 4100 for configuring one or moresignal modules 2614, according to some embodiments.

Method 4100 shall be described with reference to FIG. 26. However,method 4100 is not limited to that example embodiment.

In 4102, signal configuration module 2802 can receive one or more signalprocessing specifications. A signal processing specification may specifya base signal to process, the lengths of input and output packet queuesfor a signal module 2614, a digital signal processing function toprocess the base signal, and one or more associated parameters for thedigital signal processing function. In some embodiments, signalconfiguration module 2802 can receive a signal processing specificationfrom a file stored in memory. In some other embodiments, signalconfiguration module 2802 can receive a signal processing specificationfrom a GUI that enables a user to manually enter the signal processingspecification.

In 4104, signal configuration module 2802 dispatches the one or moresignal processing specifications to signal factory module 2804.

In 4106, signal factory module 2804 generates a signal module 2614 foreach signal processing specification. 4106 can be performed by method4200 in FIG. 42.

FIG. 42 is a flowchart for a method 4200 for generating a signal module2614 from a signal processing specification, according to someembodiments.

Method 4200 shall be described with reference to FIG. 26. However,method 4200 is not limited to that example embodiment.

In 4202, signal factory module 2804 generates an input packet queue 2902of the signal module 2614 based on the signal processing specificationin 4106 of FIG. 41. For example, signal factory module 2804 generates aninput packet queue 2902 by creating a queue data structure of the lengthspecified in the signal processing specification.

In 4204, signal factory module 2804 generates an output packet queue2906 of the signal module 2614 based on the signal processingspecification. For example, signal factory module 2804 generates anoutput packet queue 2806 by creating a queue data structure of thelength specified in the signal processing specification.

In 4206, signal factory module 2804 generates a DSP 2904 of the signalmodule 2614 using DSP factory module 2808 based on the signal processingspecification. Specifically, signal factory module 2804 can request DSPfactory module 2808 to generate the DSP 2904 based on the digitalprocessing function and one or more signal processing parametersspecified in the signal processing specification. For example, DSPfactory module 2808 can generate DSP 2904 based on a low-pass filterfunction and a specific cutoff frequency specified in the signalprocessing specification.

In 4207, signal factory module 2804 connects the generated input packetqueue 2902, the generated DSP 2904, and the generated output packetqueue 2906 of the signal module 2614. Specifically, signal factorymodule 2804 connects the output of the input packet queue 2902 to theinput of DSP 2904. Signal factory module 2804 further connects theoutput of DSP 2904 to the input of output packet queue 2906.

In 4210, signal factory module 2804 configures input packet queue 2902to receive packets dispatched from packet dispatcher 2610. In someembodiments, signal factory module 2804 can add a rule to a lookup tableassociated with packet dispatcher 2610. The rule may specify thatpackets associated with a given signal can be processed by a givensignal module 2614.

In 4212, signal factory module 2804 uses DSP delay equalizer 2806 toequalize the associated processing delays of each generated signalmodule 2614 such that each signal module 2614 outputs a processed packetto its output packet queue 2906 at the same time. 4210 can be performedby method 4300 in FIG. 43.

FIG. 43 is a flowchart for a method 4300 for equalizing the processingdelay associated with each DSP 2904 of the one or more signal modules2614, according to some embodiments.

Method 4300 shall be described with reference to FIG. 26. However,method 4300 is not limited to that example embodiment.

In 4302, DSP delay equalizer 2806 requests the processing delayassociated with each DSP 2904 of the one or more signal modules 2614.DSP delay equalizer 2806 can request the processing delay of a DSP 2904using an API of its associated signal module 2614.

In 4304, DSP delay equalizer 2806 receives the processing delay of a DSP2904 from each of the one or more signal modules 2614.

In 4306, DSP delay equalizer 2806 determines a maximum processing delayamong the one or more received processing delays.

In 4308, DSP delay equalizer 2806 sets a DSP 2904 of each of the one ormore signal modules 2614 to the maximum processing delay. For example,DSP delay equalizer 2806 can set the processing delay of a DSP 2904 ofeach signal module 2614 using an API. In response, each DSP 2904 can bedesigned to process a packet using its digital processing function andoutput the processed packet to output packet queue 2906 at the end ofthe maximum processing delay. In some embodiments, a DSP 2904 can blockits output to output packet queue 2906 if it completes processing apacket using its digital processing function prior to the end of themaximum processing delay.

FIG. 44 is a flowchart for a method 4400 for receiving one or moresignal samples for one or more signals using input module 2604,according to some embodiments.

Method 4400 shall be described with reference to FIG. 26. However,method 4400 is not limited to that example embodiment.

In 4402, input module 2604 receives signal samples for a base signalfrom a hardware device (e.g., an electrode attached to a patient) ordata stored in a computer file. For example, the computer file maycontain a previously recorded session of signal samples received from ahardware device. As would be appreciated by a person of ordinary skillin the art, input module 2604 can simultaneously receive signal samplesfor multiple based signals.

In 4404, input module 2604 dispatches the received signal samples topacketizer 2606.

FIG. 45 is a flowchart for a method 4500 for converting one or moresignal samples to one or more packets using packetizer 2606, accordingto some embodiments.

Method 4500 shall be described with reference to FIG. 26. However,method 4500 is not limited to that example embodiment.

In 4502, packetizer 2606 receives one or more signal samples from inputmodule 2604.

In 4504, packetizer 2606 can optionally preprocess the one or moresignal samples. For example, packetizer 2606 can convert the binaryvalues of the one or more signal samples to their corresponding physicalvalues. As would be appreciated by a person of ordinary skill in theart, packetizer 2606 can perform various other types of preprocessing.

In 4506, packetizer 2606 generates a packet containing the one or moresignal samples for a given base signal. Packetizer 2606 can store apredefined number of signal samples in the packet. In some embodiments,packetizer 2606 can use timer 2605 to ensure that each packet containsthe same number of signal samples. Specifically, packetizer 2606 canstore signal samples received from input module 2604 into the packetuntil timer 2605 is triggered.

In 4508, packetizer 2606 assigns a tag to the generated packet. The tagmay correspond to a time period in which the one or more signal samplesin the packet were received. Packetizer 2606 can assign a new tag toeach subsequent packet. For example, packetizer 2606 can first generatea packet containing sixteen (16) signal samples for a given base signal.In this case, packetizer 2606 can store the first set of signal samplesin a packet with a tag of 0. Packetizer 2606 can store the second set ofsignal samples in a packet with a tag of 15. Packetizer 2606 can storethe subsequent sets of signal samples in packets with tags of 31, 47,64, etc.

FIG. 46 is a flowchart for a method 4600 for dispatching a packetcontaining one or more signal samples to queueing module 2608, accordingto some embodiments.

Method 4600 shall be described with reference to FIG. 26. However,method 4600 is not limited to that example embodiment.

In 4602, packetizer 2606 determines a base signal associated with anewly generated packet.

In 4604, packetizer 2606 determines a queue 2702 in queuing module 2608associated with the determined base signal. Packetizer 2606 candetermine that a queue 2702 is associated with the determined basesignal using a lookup table.

In 4606, packetizer 2606 dispatches the packet containing the one ormore signal samples to the determined queue 2702.

FIG. 47 is a flowchart for a method 4700 for dispatching a packet fromqueuing module 2608 to a signal module 2614 associated with the packet,according to some embodiments.

Method 4700 shall be described with reference to FIG. 26. However,method 4700 is not limited to that example embodiment.

In 4702, packet dispatcher 2610 continuously scans a queue 2702 inqueueing module 2608.

In 4704, packet dispatcher 2610 detects a new packet in the queue 2702.

In 4706, packet dispatcher 2610 determines one or more signal modules2614 in global signals table 2612 that are designed to process the newpacket. Because the new packet can be dispatched to multiple signalmodules 2614 (e.g., multiple copies or “instances” of the packet), thebase signal associated with the packet can be simultaneously processedusing different digital processing functions of the signal modules 2614.

In some embodiments, packet dispatcher 2610 can determine one or moresignal modules 2614 that are designed to process an instance of the newpacket using global signals table 2612. For example, global signalstable 2612 can be a fixed size array. Each element of the array can beassociated with a given base signal, and thus a given a queue 2702.Moreover, each element of the array can be a fixed size array itself.Each element of this subarray can be associated with a given signalmodule 2614. Thus, packet dispatcher 2610 can determine one or moresignal modules 2614 that are designed to process the new packet bychecking the corresponding element in the subarray associated with thebase signal of the new packet.

In some other embodiments, packet dispatcher 2610 can determine the oneor more signal modules 2614 that are designed to process the new packetusing a lookup table. Specifically, the lookup table may map the queue2702 to one or more signal modules 2614.

In 4706, packet dispatcher 2610 dispatches the new packet to thedetermined one or more signal modules 2614 in global signals tables 2612for processing. Specifically, packet dispatcher 2610 inserts the newpacket into the input packet queues 2902 of the determined one or moresignal modules 2614.

FIG. 48 is a flowchart for a method 4800 for processing a packet using asignal module 2614 associated with the packet, according to someembodiments.

Method 4800 shall be described with reference to FIG. 26. However,method 4800 is not limited to that example embodiment.

In 4802, DSP 2904 detects whether a new packet is available in the inputpacket queue 2902 of the signal module 2614. In some embodiments, DSP2904 can scan the input packet queue 2902 for a new packet to process.In some other embodiments, DSP 2904 can get a notification that a newpacket is available in the input packet queue 2902.

In 4804, DSP 2904 retrieves the new packet from input packet queue 2902of the signal module 2614.

In 4806, DSP 2904 processes the new packet using its associated digitalsignal processing function. Specifically, DSP 2904 can apply its digitalprocessing function to the one or more signal samples in the packet. Insome embodiments, DSP 2904 can control how it processes the packet usingits digital processing function based on one or more signal processingparameters designed for DSP 2904.

In 4808, DSP 2904 outputs the processed packet to output packet queue2906. In some embodiments, DSP 2904 can output the processed packet tooutput packet queue 2906 based on its designed maximum processing delay.

FIG. 49 is a flowchart for a method 4900 for displaying a processedpacket to a display screen using display module 2618, according to someembodiments.

Method 4900 shall be described with reference to FIG. 26. However,method 4900 is not limited to that example embodiment.

In 4902, display module 2618 determines what one or more signal modules2614 from which to display processed packets. In some embodiments,display modules 2618 can determine what one or more signal modules 2614to display processed packets from by maintaining references to theoutput packet queues 2906 of the one or more signal modules 2614.Display module 2618 can store the references in local signal table 3002.

In 4904, display module 2618 detects that a new packet is available inan output packet queue 2906 of one of the determined signal modules2614.

In 4906, display module 2618 receives the new packet from the outputpacket queues 2906 of the one of the determined signal modules 2614.

In 4908, display module 2618 determines a tag associated with newpacket.

In 4910, display module 2618 receives new packets from the other outputpacket queues 2906 that match the determined tag.

In 4912, display module 2618 simultaneously displays the received newpackets for one or more signal modules to a display screen. Becausedisplay module 2618 displays new packets having the same tag, displaymodule 2618 synchronizes the display of the signals associated with thenew packets.

Methods 4000, 4100, 4200, 4300, 4400, 4500, 4600, 4700, 4800, 4900 canbe performed by processing logic that can comprise hardware (e.g.,circuitry, dedicated logic, programmable logic, microcode, etc.),software (e.g., instructions executing on a processing device), or acombination thereof. It is to be appreciated that not all steps may beneeded to perform the disclosure provided herein. Further, some of thesteps may be performed simultaneously, or in a different order thanshown in FIGS. 40-49, as will be understood by a person of ordinaryskill in the art.

Computer System Implementation

Various embodiments can be implemented, for example, using one or morewell-known computer systems, such as computer system 5000 shown in FIG.50. One or more computer systems 5000 can be used, for example, toimplement any of the embodiments discussed herein, as well ascombinations and sub-combinations thereof.

Computer system 5000 can include one or more processors (also calledcentral processing units, or CPUs), such as a processor 5004. Processor5004 can be connected to a communication infrastructure or bus 5006.

Computer system 5000 can also include user input/output device(s) 5003,such as monitors, keyboards, pointing devices, etc., which cancommunicate with communication infrastructure 5006 through userinput/output interface(s) 5002.

One or more of processors 5004 can be a graphics processing unit (GPU).In an embodiment, a GPU can be a processor that is a specializedelectronic circuit designed to process mathematically intensiveapplications. The GPU can have a parallel structure that is efficientfor parallel processing of large blocks of data, such as mathematicallyintensive data common to computer graphics applications, images, videos,etc.

Computer system 5000 can also include a main or primary memory 5008,such as random access memory (RAM). Main memory 5008 can include one ormore levels of cache. Main memory 5008 can have stored therein controllogic (e.g., computer software) and/or data.

Computer system 5000 can also include one or more secondary storagedevices or memory 5010. Secondary memory 5010 can include, for example,a hard disk drive 5012 or a removable storage device or drive 5014.Removable storage drive 5014 can be a floppy disk drive, a magnetic tapedrive, a compact disk drive, an optical storage device, tape backupdevice, or any other storage device/drive.

Removable storage drive 5014 can interact with a removable storage unit5018. Removable storage unit 5018 can include a computer usable orreadable storage device having stored thereon computer software (controllogic) or data. Removable storage unit 5018 can be a floppy disk,magnetic tape, compact disk, DVD, optical storage disk, or any othercomputer data storage device. Removable storage drive 5014 can read fromor write to removable storage unit 5018.

Secondary memory 5010 can include other means, devices, components,instrumentalities, or other approaches for allowing computer programs orother instructions or data to be accessed by computer system 5000. Suchmeans, devices, components, instrumentalities, or other approaches caninclude, for example, a removable storage unit 5022 and an interface5020. Examples of the removable storage unit 5022 and the interface 5020can include a program cartridge and cartridge interface (such as thatfound in video game devices), a removable memory chip (such as an EPROMor PROM) and associated socket, a memory stick and USB port, a memorycard and associated memory card slot, or any other removable storageunit and associated interface.

Computer system 5000 can further include a communication or networkinterface 5024. Communication interface 5024 can enable computer system5000 to communicate and interact with any combination of externaldevices, external networks, external entities, etc. (individually andcollectively referenced by reference number 5028). For example,communication interface 5024 can allow computer system 5000 tocommunicate with external or remote devices 5028 over communicationspath 5026, which can be wired or wireless (or a combination thereof),and which can include any combination of LANs, WANs, the Internet, etc.Control logic or data can be transmitted to and from computer system5000 via communications path 5026.

Computer system 5000 can also be any of a personal digital assistant(PDA), desktop workstation, laptop or notebook computer, netbook,tablet, smart phone, smart watch or other wearable, appliance, part ofthe Internet-of-Things, or embedded system, to name a few non-limitingexamples, or any combination thereof.

Computer system 5000 can be a client or server, accessing or hosting anyapplications or data through any delivery paradigm, including but notlimited to remote or distributed cloud computing solutions; local oron-premises software (“on-premise” cloud-based solutions); “as aservice” models (e.g., content as a service (CaaS), digital content as aservice (DCaaS), software as a service (SaaS), managed software as aservice (MSaaS), platform as a service (PaaS), desktop as a service(DaaS), framework as a service (FaaS), backend as a service (BaaS),mobile backend as a service (MBaaS), infrastructure as a service (IaaS),etc.); or a hybrid model including any combination of the foregoingexamples or other services or delivery paradigms.

Any applicable data structures, file formats, and schemas in computersystem 5000 can be derived from standards including but not limited toJavaScript Object Notation (JSON), Extensible Markup Language (XML), YetAnother Markup Language (YAML), Extensible Hypertext Markup Language(XHTML), Wireless Markup Language (WML), MessagePack, XML User InterfaceLanguage (XUL), or any other functionally similar representations aloneor in combination. Alternatively, proprietary data structures, formatsor schemas can be used, either exclusively or in combination with knownor open standards.

In some embodiments, a tangible, non-transitory apparatus or article ofmanufacture including a tangible, non-transitory computer useable orreadable medium having control logic (software) stored thereon can alsobe referred to herein as a computer program product or program storagedevice. This includes, but is not limited to, computer system 5000, mainmemory 5008, secondary memory 5010, and removable storage units 5018 and5022, as well as tangible articles of manufacture embodying anycombination of the foregoing. Such control logic, when executed by oneor more data processing devices (such as computer system 5000), cancause such data processing devices to operate as described herein.

Based on the teachings contained in this disclosure, it will be apparentto persons skilled in the relevant art how to make and use embodimentsof this disclosure using data processing devices, computer systems, orcomputer architectures other than that shown in FIG. 50. In particular,embodiments can operate with software, hardware, and/or operating systemimplementations other than those described herein.

CONCLUSION

The EP recording system disclosed herein effectively removes noise andremoves or isolates unwanted large signals while preserving relevantcomponents of raw small signals, that is, while preserving integrity oforiginal information in an EP environment. Conventional EP systems cansuccessfully filter out noise but may also filter out signal componentswith the noise that a medical team desires to see. Conventional EPsystems can also generate and introduce additional noise and unwantedartifacts not originally present in the raw signals with well-meaningsoftware filtering algorithms. Even when conventional EP systems utilizestate-of-the-art noise reduction practices, conventional EP systemscannot effectively collect clean small signals with high confidence inthe presence of simultaneous large-signal procedures such asdefibrillation and ablation. This is because conventional EP systems donot have a comprehensive signal acquisition and filtering solutionacross the relevant frequency ranges—low (e.g., 0 to 100 Hz), mid (e.g.,above 100 Hz to below 300 kHz), and high (e.g., above and including 300kHz)—and cannot effectively handle simultaneous signals that differ by100s or 1000s of orders of magnitude. In comparison, the EP recordingsystem disclosed herein integrates and applies novel hardware circuitry,software methods, and system topologies to remove unwanted signals butpreserve original signal waveforms across the relevant frequencies forsignals found in an EP environment.

The disclosed EP system does not have to make tradeoffs thatconventional EP systems have to make. Rather, the disclosed EP systemallows aspects of hardware and software to perform in tandem, in orderto simultaneously: (1) run amplifiers at high gain to see small signals,(2) prevent both clipping and saturation by minimizing destructivelarge-signal filtering in hardware to see the large signals at the sametime, (3) process the signals, separating them from each other inindependent displays, removing any remaining noise, and synchronizingseparated signals, and finally (4) enable a user to manipulate andanalyze both large and small signals so that signal artifacts and eventscan be accurately time-and-event correlated.

The exemplary signals 2200 of FIGS. 22A-22B illustrate these concepts,showing the improvement in the visualization of an ECG or IC cardiacsignal in the presence of large transients, ablation signals,defibrillation signals, and EP environment noise after being acquired,filtered, and processed by the EP system disclosed herein. FIG. 22Ashows the removal of noise from both small and large signals, and theavoidance of clipping in the processing of large signals. A conventionalEP system may provide a noisy cardiac signal 2203 and artificially clipa signal 2202 to limit the amplitude of a displayed signal to avoid theeffects of saturation. The disclosed EP system acquires and clearlydisplays both weak 2214 and strong 2205 signals. With the disclosed EPsystem, there is no need for artificial clipping, and a strong signal2204 is fully defined (not clipped).

FIG. 22B illustrates the EP system's ability to reveal low-amplitudecardiac signals and micro-components of relevant random artifacts of anEP signal in the presence of noise and large-signal procedures. Thewindow 2216 illustrates a noisy signal 2208 with both the high andlow-amplitude micro-components 2206 of the desired signal revealed bythe disclosed EP system. In comparison, as shown in window 2218, aconventional EP system may not as successfully reveal both low andhigh-amplitude micro-components of the desired signal. With noisiersignals, a low-amplitude micro-component 2210 of the desired signal canbe revealed but is more apt to be lost amongst the noise 2212 in aconventional EP system. A high-amplitude micro-component 2211 of thedesired signal may be lost by artificial clipping in a conventional EPsystem.

FIG. 22C illustrates the ability of the disclosed EP system to remove 60Hz noise 2220, without saturation or delayed recovery, while preservingthe component 2222 of the 60 Hz signal that belongs to the originalwaveform 2224. Specifically, component 2222, of the original waveform2224, which occurs at the same time as the artifact 2220, is not lost.In other words, when large signals simultaneously overlap small signals,the disclosed EP system can identify, acquire, and process both cleanly.

It is to be appreciated that the Detailed Description section, and notany other section, is intended to be used to interpret the claims. Othersections can set forth one or more but not all exemplary embodiments ascontemplated by the inventor(s), and thus, are not intended to limitthis disclosure or the appended claims in any way.

While this disclosure describes exemplary embodiments for exemplaryfields and applications, it should be understood that the disclosure isnot limited thereto. Other embodiments and modifications thereto arepossible, and are within the scope and spirit of this disclosure. Forexample, and without limiting the generality of this paragraph,embodiments are not limited to the software, hardware, firmware, orentities illustrated in the figures or described herein. Further,embodiments (whether or not explicitly described herein) havesignificant utility to fields and applications beyond the examplesdescribed herein.

Embodiments have been described herein with the aid of functionalbuilding blocks illustrating the implementation of specified functionsand relationships thereof. The boundaries of these functional buildingblocks have been arbitrarily defined herein for the convenience of thedescription. Alternate boundaries can be defined as long as thespecified functions and relationships (or equivalents thereof) areappropriately performed. Also, alternative embodiments can performfunctional blocks, steps, operations, methods, etc. using orderingsdifferent than those described herein. This disclosure also extends tomethods associated with using or otherwise implementing the features ofthe disclosed hardware and systems herein.

References herein to “one embodiment,” “an embodiment,” “an exemplaryembodiment,” or similar phrases, indicate that the embodiment describedcan include a particular feature, structure, or characteristic, butevery embodiment cannot necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it would be within the knowledge of persons skilled in therelevant art to incorporate such feature, structure, or characteristicinto other embodiments whether or not explicitly mentioned or describedherein. Additionally, some embodiments can be described using theexpression “coupled” and “connected,” along with their derivatives.These terms are not necessarily intended as synonyms for each other. Forexample, some embodiments can be described using the terms “connected”or “coupled” to indicate that two or more elements are in directphysical or electrical contact with each other. The term “coupled,”however, can also mean that two or more elements are not in directcontact with each other, but yet still co-operate or interact with eachother.

The breadth and scope of this disclosure should not be limited by any ofthe above-described exemplary embodiments, but should be defined only inaccordance with the following claims and their equivalents.

What is claimed is:
 1. A system for displaying electrocardiogram (ECG)and intracardiac (IC) signals, comprising: a plurality of inputsconfigured to receive electrophysiological signals, theelectrophysiological signals comprising first signals from a catheterwhen disposed inside a heart of a patient and second signals from atleast three limb electrodes, when each limb electrode is disposed on arespective different limb of the patient; a differential amplifier stagecoupled to the plurality of inputs and configured to output adifferential signal representing electrophysiological activity; aright-leg drive (RLD) circuit electrically coupled to the at least twolimb electrodes and configured to output a right-leg drive output signalto a right leg electrode when located on the patient's right leg; ananalog-to-digital converter module configured to convert thedifferential signal representing electrophysiological activity to adigitized electrophysiological signal; and one or more processorsconfigured to format the digitized electrophysiological signal to be atleast one of displayed on a display unit and stored.
 2. The system ofclaim 1, wherein the right-leg drive circuit is configured to remove acommon mode voltage from the second signals received from the at leastthree limb electrodes.
 3. The system of claim 1, wherein the right-legdrive circuit has a common mode configured to reject power line noise ata first harmonic frequency and a third harmonic frequency.
 4. The systemof claim 1, wherein the right-leg drive circuit is configured to preventcurrent having an amplitude greater than one microampere from flowing tothe right leg electrode.
 5. The system of claim 1, wherein the at leastthree limb electrodes comprise a right arm electrode, a left armelectrode, and a left leg electrode.
 6. The system of claim 3, whereinthe first harmonic frequency is 60 Hz and the third harmonic frequencyis 180 Hz.
 7. The system of claim 3, wherein the right leg drive circuitis further configured to combine the second signal from the at least twolimb electrodes by averaging the electrophysiological signals from theright arm electrode, the left arm electrode, and the left leg electrode.8. A system for displaying electrocardiogram (ECG) and intracardiac (IC)signals, comprising: a Wilson Central Terminal (WCT) circuit configuredto be coupled to three limb electrodes; a right leg drive circuitconfigured to be coupled to a fourth limb electrode; and a twin-Tnetwork, coupled to the right leg drive circuit, comprising a firsttwin-T circuit coupled to a second twin-T circuit and an operationalamplifier; wherein a node of the first twin-T circuit is coupled to afirst input of the operational amplifier, at least two of the three limbelectrodes are coupled to a second input of the operational amplifier,and an output of the operational amplifier is coupled to an input of theright leg drive circuit, and wherein a node of the second twin-T circuitis coupled to the output of the operational amplifier.
 9. The system ofclaim 8, wherein the WCT circuit provides a unipolar input reference forsingle catheter inputs.
 10. The system of claim 8, wherein the right legdrive circuit is configured to remove common mode voltage from a signalreceived at the input of the right leg drive circuit.
 11. The system ofclaim 8, wherein the right leg drive circuit is configured to preventcurrent having an amplitude greater than one microampere from flowing tothe fourth limb electrode.
 12. The system of claim 8, wherein the twin-Tnetwork comprises a notch filter in a feedback path of the twin-Tnetwork.
 13. The system of claim 8, wherein the twin-T network isconfigured to provide enhanced common mode rejection of a first harmonicfrequency and a third harmonic frequency of power mains.
 14. The systemof claim 8, wherein a first harmonic frequency is 60 Hz and a thirdharmonic frequency is 180 Hz.
 15. The system of claim 8, wherein theright-leg drive circuit is configured to remove a common mode voltagefrom a signal received from the three limb electrodes.
 16. The system ofclaim 8, wherein the twin-T network is configured to produce a firstpeak and a second peak at the output of the operational amplifier,wherein the first peak has a first center frequency located at a firstharmonic frequency and the second peak has a second center frequencylocated at a third harmonic frequency.
 17. A method of filteringelectrophysiology signals in a patient using at least two limbelectrodes coupled to different limbs of the patient and anelectrophysiology system, comprising: receiving at least two signalsfrom the least two limb electrodes at a first input of an operationalamplifier; enhancing a first harmonic frequency and a third harmonicfrequency of power mains associated with the electrophysiology system atan output of the operational amplifier; and providing the output of theoperational amplifier through at least two twin-T circuits and into asecond input of the operational amplifier.
 18. The method of claim 17,further comprising applying the output of the operational amplifier to aright leg drive circuit.
 19. The method of claim 17, wherein the firstharmonic frequency is 60 Hz and the third harmonic frequency is 180 Hz.